The Humming Beneath the Hills

I lived in a small flat above my uncle's independent garage in a former industrial town in South Wales. Its two rooms smelt permanently of engine oil and brake fluid. The smell seeped through the floorboards no matter how many towels I wedged beneath the door.

At night, I would lie awake listening to the vehicle ramps hiss and clank, even though the garage was shut and Uncle Graham Price had gone home hours before. The noises were only echoes, I think. Ghosts of the day's work trapped in the walls.

Weekends were my escape. Every other Saturday, and sometimes three weekends running if I could manage it, I met Oliver Shaw and Callum Morgan at a forestry trail near Mynydd Du. We had been camping together since we were ten.

Five years of the same footpaths, the same campsite in the Brecon Beacons, the same routine that felt more like home than anywhere else.

Oliver came from the sort of money that funded hospital wings and put family names on university buildings. His parents hovered over every aspect of his life with the anxious intensity of people who had waited too long for a child and could not quite believe their luck would last. Our camping trips were his only unsupervised hours.

Even those came with a list of conditions that changed every week. A whistle, a first-aid kit, a personal locator beacon, a location-sharing mobile and scheduled calls every four hours.

Callum was different. He lived with his grandfather, Idris Morgan, in a remote stone cottage so far into the hills that Royal Mail did not deliver directly to it.

His parents had died in a car crash when he was six. Black ice on the A4069 over the Black Mountain. The sort of thing that happened every winter in the hills, yet always seemed impossible until it happened to your family. Idris had raised him ever since.

It was just the two of them in that cottage, with no television and an old wireless that received only medium-wave stations in clear weather.

The summer we turned fifteen, everything changed. Oliver's parents banned our usual campsite after a forestry officer warned of adders near the trails and reported several unstable trees. That was enough to send their protective instincts into overdrive.

They wanted Oliver at home for the summer, or somewhere supervised: a residential tennis course, intensive GCSE revision tuition, anything that kept him within reach.

We were sitting on the kerb outside a supermarket when Oliver told us, his voice tight with frustration.

"They won't budge. I've tried everything."

Callum was quiet for a long moment. He picked at the scar on his forearm, an old habit whenever he was thinking something through.

"You could camp on my grandfather's land."

"Could we?"

Oliver's whole face changed.

"He's got about eighty hectares. We'd be out of everyone's way." Callum hesitated. "He might not like the idea, but he won't say no."

I should have asked more questions then. I should have wondered why Callum seemed uncertain about his own suggestion. But I was fifteen and desperate for those woods, for distance from the garage and from Uncle Graham's silent disappointment whenever he looked at me.

Idris Morgan was waiting on the porch when we arrived that Friday evening. He stood in the fading light as though he had been carved from the same weathered stone as his cottage. He was sixty-eight, broad and solid after decades of manual labour, with eyes that followed our approach from nearly a hundred metres away.

"Grandad, these are my friends, Oliver and Aaron."

Idris studied us without speaking. His silence had weight.

"We were hoping to camp here this weekend," Callum said. His voice remained steady, but I could hear the tension beneath it. "Just the three of us."

Idris's gaze moved to Oliver, then to me, then back to Callum.

"Your friends know the rules?"

"I'll tell them."

Another long silence followed. Then Idris stepped aside and jerked his head towards the woods beyond the cottage.

"The eastern ridge is out of bounds. There's an old nineteenth-century coal level driven into the hillside up there. The main entrance was sealed before our family bought this land, but that never stopped the sounds, and nobody knows every way into those workings."

He looked at each of us in turn.

"If you hear anything coming from it - voices, music, someone calling for help - you ignore it and come straight back here. Understood?"

The hair rose on my arms, although I could not have said why.

"Understood," we said.

"Doesn't matter what you think you've heard. Doesn't matter if it sounds as though somebody needs help. You stay away from that level. No arguments."

Oliver nodded quickly. I did the same.

Idris retreated into the cottage without another word, and the door banged shut behind him.

We followed Callum along a narrow path winding through dense undergrowth. Rusted signs littered the smallholding. NO TRESPASSING notices had been hammered to trees at intervals of about fifteen metres, some so old that their lettering had faded to ghosts. Heavy chains blocked side paths, wrapped around trunks and secured with padlocks seized by age and weather.

"Your grandfather really doesn't want visitors," Oliver said.

Callum did not answer.

I took it for an old man's paranoia. Idris had lived alone too long and become strange about his land, the way people sometimes did when they had nothing but time and solitude. The signs were excessive, certainly, but harmless. Eccentricity, not danger.

The woods opened beside a stream running fast and clear over smooth stones. Tall conifers surrounded the clearing, their branches so dense overhead that the light came through in scattered patches. Mist clung to the hollows between the trees and gave everything a soft, dreamlike quality.

"Here," Callum said. "We can camp here."

We dropped our rucksacks and scattered to gather firewood. The freedom struck me all at once. No adults watching, no checking the time, nobody asking where I had been or why I had taken so long. Just us, the woods and three whole days ahead.

Oliver found a fallen branch and began breaking it into manageable pieces.

"This is perfect. Your grandad's actually all right, letting us stay."

Callum did not answer. He was building a fire ring with stones from the stream, every movement careful and methodical.

We worked until dark, making something that felt permanent even though we would dismantle it in three days: a proper fire ring, a cooking place with flat stones arranged just so, sleeping spots cleared of roots and rocks, and our tents positioned to catch the morning sun. The stream provided constant background music, a sound that ought to have been peaceful.

I remember lying in my tent that first night, listening to the water and the wind in the trees and thinking it was the best weekend we had ever had. I remember feeling safe.

The humming began at about seven on Saturday evening, as the light thinned between the trees.

I was crouched beside the fire, feeding it smaller branches to keep the flame steady, when the sound reached me. At first I felt it more than heard it: a vibration in my chest that did not match my heartbeat. It took several seconds to realise that the sensation came from outside my body.

"Can you hear that?"

Oliver stood near his tent with his head tilted.

Callum had gone completely still. He had been arranging his sleeping bag, but now he was frozen half inside the tent and half outside it, one hand gripping the fabric so tightly that his knuckles showed white even in the failing light.

The humming became clearer. It was one steady, mechanical note coming from somewhere east of our campsite, from the ridge Idris had warned us about.

"That's the level," Callum said flatly.

He pulled himself out of the tent and stood with his shoulders rigid.

"We need to move."

"Move?" Oliver laughed, but it sounded forced. "We've just spent three hours setting this up."

"I don't care."

Callum was already striding towards his rucksack, his movements jerky and too quick.

"We're packing. We're going back to Grandad's cottage."

I stood and brushed bark dust from my hands. The humming had not changed pitch or varied at all. That single continuous note simply rolled down from the ridge and through the darkening woods.

"Callum, what is it?"

"This land's been in my family for four generations." He did not look at either of us. He yanked his sleeping bag out and stuffed it into his rucksack without rolling it. "My great-grandfather bought it in 1922. That level was already here. The main entrance was already sealed."

Oliver folded his arms.

"So?"

"So they sealed it for a reason."

Callum finally looked up. His face had become so pale that something cold settled in my stomach.

"In the 1970s, three people disappeared over two years. They went near the old workings and never came back. Search teams found nothing. No bodies, no equipment. Nothing."

The humming continued without change. I realised I could now feel it through my trainers, a faint vibration in the earth itself.

"What's that got to do with the noise?" I asked.

I tried to sound reasonable, although my mouth had gone dry.

Callum jerked his chin towards the eastern ridge.

"It starts every few nights. Sometimes it's only humming. Sometimes you hear machinery underground. Old equipment running. Metal striking metal. Sometimes there are voices."

"Voices?" Oliver asked, his scepticism plain.

"Calling for help."

Callum had finished cramming his kit into his rucksack and was dismantling his tent, wrenching the pegs out with short, violent tugs.

"Grandad taught me when I was seven. If you hear anything from those workings, you don't investigate. You don't call back. You don't even acknowledge it. You get away and wait for it to stop."

I glanced towards the ridge, but the dense trees hid everything. There was only darkness gathering between the trunks and that steady, relentless hum threading through it all.

"How long does it usually last?"

"Hours." Callum shoved his collapsed tent into its bag without folding it. "Sometimes all night."

The humming changed.

The pitch remained constant, but the rhythm began to pulse: three seconds on, one second off. Three seconds on, one second off, regular as a heartbeat.

The vibration in the ground matched it and grew stronger with each cycle. I felt it in my bones, in my jaw and in the hollow spaces behind my eyes.

"Jesus."

The word escaped before I could stop it.

Oliver had not moved. He still stood beside his tent with his arms crossed, but his expression was less certain now.

"It's old machinery settling. Underground spaces do that. Expansion, contraction, changes in air pressure."

"Then we can listen to it settle from my grandad's cottage."

Callum had his rucksack on. He stamped out the fire, scattering burning wood across the stone ring.

"I'm going. You two can do what you like."

The pulsing hum grew louder and faster. The one-second silences shortened to half a second and then vanished. The vibration became constant again, stronger now, deep enough to make my teeth ache.

"This is ridiculous." Oliver's voice carried an edge I recognised, the same one he used when his parents imposed a new restriction or anyone tried to tell him what he could and could not do. "You're letting ghost stories dictate our whole weekend."

"Oliver." I stepped towards him. "Maybe we should-"

"No."

He moved abruptly to his rucksack and pulled out the heavy six-cell high-powered torch his mother had insisted he bring. It was as weighty as a club.

"I'm not running away from superstition. There's a rational explanation for everything, and I'm going to prove it."

Callum stopped moving.

"Don't."

"Watch me."

Oliver switched on the torch. Its beam cut white and hard through the gathering darkness.

"Abandoned workings, old equipment and the acoustic properties of tunnels amplifying ordinary settling noises. That's all it is."

"Oliver, please." Callum's voice cracked. "Please don't do this."

"I'll be back in twenty minutes."

Oliver was already walking east through the trees, towards the ridge and the relentless mechanical hum.

"You'll see. There's nothing supernatural about it."

"Oliver!"

Callum lunged after him, but Oliver was faster. He broke into a jog, the torch beam jumping wildly between the trunks.

The humming changed.

It did not fade or alter gradually. The mechanical tone stopped in the middle of a pulse, and something else replaced it.

A wail came from everywhere and nowhere, deep, resonant and wrong in a way that bypassed thought and reached the primitive part of my mind that understood predators and prey, danger and safety.

It came from the earth. It rose through the soles of my trainers and along my legs, vibrated inside my ribcage and blurred my vision.

Birds burst from the trees in a black cloud, their wings beating frantically against branches. Something crashed through the undergrowth to my left, perhaps a deer, perhaps several running blind. Smaller shapes scattered in every direction, rabbits and squirrels fleeing in absolute terror, indifferent to humans, fire or anything except escape from that sound.

Oliver stopped. I could see him about twenty metres into the trees, his torch beam fixed on the ground and his whole body rigid.

The wailing continued. I could not breathe around it.

Callum turned back towards the stream, where we had left everything. His rucksack was already on his shoulders, its straps drawn tight across his chest. The sound vibrated through my teeth.

"This is on me," he said.

His voice was flat and dead.

"I brought you here."

Oliver's torch still pointed at the ground twenty metres into the trees. He had not moved since the noise changed. His shoulders were hunched around his ears.

"We need to get to the cottage," I said.

My jaw hurt from clenching it.

"All three of us. Now."

Callum shook his head. The wailing made his expression difficult to see because my vision blurred with every pulse, but I saw enough: the set of his mouth and the way his hands hung loose at his sides instead of tightening into fists.

He had made a decision.

"You two get to the cottage," he said. "Stay on the porch. Don't go inside. Don't hide in the woods. Stay on the porch, where Grandad can see you when he comes looking."

"What are you-"

"Oliver shouldn't have gone towards it."

Callum raised his voice to cut through the wailing.

"But I shouldn't have brought you here at all. I knew better. Grandad told me a hundred times never to bring anyone onto this land. Never to let anyone hear it."

The wailing shifted again, becoming lower, less like machinery and more like something attempting to form words.

Callum began to walk. Not towards Oliver and not towards the cottage, but east through the trees, towards the ridge.

"I can fix this," he shouted back. "I know what it wants."

My legs unlocked. I ran after him and caught his arm. His jacket was soaked with sweat despite the cool air.

"You can't go there," I said. "Your grandfather said-"

"My grandad's rules are for people who don't live here."

Callum tore himself free. His face was white and his eyes were too wide, but his hands were steady.

"I've lived on this land since I was six. It knows me."

"That doesn't make sense."

"None of this makes sense."

He was already moving again, faster now.

"But Oliver walked towards it. Oliver challenged it. Now it's awake, and it won't stop until-"

He did not finish. He broke into a run, crashing through the undergrowth towards the eastern ridge.

I heard him shouting as he went. I could not distinguish the words over the wailing, but his tone was unmistakable. He was apologising, pleading, offering something.

The wailing stopped.

It simply ended in the middle of a pulse. The sudden silence struck harder than the noise had. My ears rang with its absence. My chest felt hollow where the vibration had been.

Oliver dropped his torch. It struck the ground while still lit, its beam pointing sideways through the trees. I heard him drag in a breath as though he had been drowning.

"Callum?" His voice broke. "Callum, where-"

I seized his shoulder and spun him round.

His face was grey, not merely pale, and his pupils had contracted to pinpoints.

"The cottage," I said. "We have to get to the cottage."

We ran. We left the tents, the rucksacks and the fire ring we had built so carefully. We left Oliver's torch casting its beam across the forest floor and simply ran, stumbling over roots and rocks while branches lashed our faces.

The cottage appeared through the trees: a low stone building with a corrugated metal roof and one window glowing yellow behind its curtains. Idris's vehicle stood in the gravel yard.

We reached the porch, with its three wooden steps and railings on either side. I collapsed against the door, struggling for breath, and Oliver dropped beside me.

"We should tell his grandad," Oliver said. "Wake him. Tell him Callum ran towards-"

"Help!"

Callum's voice came clearly from the east, from the ridge.

"Help! I'm hurt! I fell in the level! I can't get out!"

Oliver stood and started down the steps.

I caught his wrist and wrenched him back. He fell heavily onto the porch boards and struck his elbow.

"That's-"

"It's him," I said.

"What are you talking about? That's Callum. He needs-"

"Listen."

The voice called again, using the same words. Precisely the same words, with the same inflection and the same pause after the first cry for help.

"Help! I'm hurt! I fell in the level! I can't get out!"

It was a perfect repetition, like a recording being played back. There was no variation, no breathlessness and no pain. It was only Callum's voice repeating those exact words in that exact rhythm.

Oliver stopped fighting my grip. His hand became slack.

"Help! I'm hurt! I fell in the level! I can't get out!"

"It isn't him," Oliver whispered.

We stayed on the porch, obeying Idris's instruction exactly. We sat with our backs against his door and our shoulders pressed together while the voice continued calling.

Every three minutes, it repeated the same words in the same tone. Beneath it was a hollow quality like wind passing through pipes.

Dawn came slowly, grey light filtering through the trees and mist rising from the ground. The voice stopped perhaps an hour before sunrise, or perhaps earlier. Time had ceased to mean much.

Idris opened the door behind us at about six. He was a heavy sleeper and hard of hearing, and the thick stone walls had kept the night's sounds from him. We fell backwards across his threshold.

He asked no questions. He looked at our faces, then past us towards the eastern ridge, and reached for his keys.

"Callum?" he said.

I could not make words work. I only shook my head.

Idris's expression did not change. He had already expected this. Perhaps he had expected it for years, ever since he taught a seven-year-old boy the rules governing the sealed coal level.

He drove us to the nearest Natural Resources Wales forestry office and called the local police from there.

Detective Inspector Gareth Vaughan arrived forty minutes later with local officers and a search coordinator. Specialist search teams and mountain rescue volunteers spent two days combing the ridge, the old level and the woods between the cottage and the sealed entrance. Police search dogs refused to approach the eastern section.

Mining-rescue specialists and police teams brought ground-penetrating radar, thermal imaging equipment and borehole cameras. They found no trace of Callum: no disturbed earth, no footprints and no torn fabric caught on branches.

The main entrance remained sealed as it had been for decades, blocked with concrete and steel reinforcement, with official danger notices bolted to the barrier.

DI Vaughan questioned us separately, then together, then separately again. I told him everything: the humming, the wailing, Callum running towards the ridge and the voice that followed.

He wrote it all down. He did not interrupt or scoff. He simply wrote.

Then he asked where Callum's body was.

That was when I understood. He thought we were lying. He believed there had been an accident, followed by panic and a cover-up. To him, the tale of sounds and imitated voices was three frightened teenagers trying to escape the consequences of something they had done.

Idris corroborated everything. He told Vaughan about the workings, the disappearances in the 1970s and the family rules concerning the eastern ridge. He explained that sealing the main entrance had never stopped the noises or the later disappearances around inaccessible and unrecorded workings. He showed him the yellowing newspaper cuttings he had kept, reports of earlier search operations that had found nothing.

Vaughan included them in his report beneath references to folklore and local superstition.

The community wanted answers. It needed them. A fifteen-year-old boy could not simply vanish, and two traumatised friends offering supernatural explanations were not enough.

Idris became the only available suspect: the grandfather who had raised his grandson in isolation on a remote smallholding; the man who had filled the boy's head with stories about dangerous mines and family rules; the last adult known to have seen Callum alive.

Crown prosecutor Helen Mercer assembled the case over six weeks after the Crown Prosecution Service authorised a murder charge. The evidence was circumstantial, but it went beyond opportunity alone. Idris's repeated warnings to Callum were presented as threats. Inconsistencies in the searches were attributed to his detailed knowledge of the land and its hidden workings. The prosecution alleged that an unobserved confrontation had taken place after we left the cottage and that Idris had used routes known only to him to conceal the body.

Our recollections differed in small details each time we were questioned, as traumatised memories often do. Mercer used those differences to undermine us and support the suggestion that Idris had coached our account.

Idris barely fought. He sat quietly through the Crown Court trial and answered questions in his gravelly voice. He could not afford a strong defence team. A solicitor instructed an overworked junior legal-aid barrister who had been practising for only three years and looked permanently exhausted.

The jury deliberated for four hours before finding Idris guilty of murder. The judge imposed the mandatory life sentence with a minimum term of fifteen years.

Idris was sixty-eight. We all knew what that meant.

Oliver stopped returning my calls three weeks after the sentence. I did not blame him. We could not look at each other without seeing Callum running into those trees or hearing his voice calling for help in that exact tone, wrong and mechanical and endlessly repeated.

I threw myself into town planning in the way some people turn to religion after a tragedy. Street grids made sense. Traffic patterns followed predictable models. Planning rules existed in black and white.

There were no grey areas and no sounds that should not exist.

I borrowed every book the local library held on town planning, transport design and population density. I spent hours at Uncle Graham's kitchen table sketching street layouts, calculating suitable distances between junctions and designing neighbourhoods that kept amenities within walking distance while reducing conflicts between vehicles and pedestrians.

Uncle Graham thought I had lost my mind. Perhaps I had.

Rural places became impossible. The sight of trees packed too closely together made my throat constrict. Open fields ending in distant lines of woodland triggered a sensation in my chest like drowning.

I planned my future around concrete and tarmac, around places where I could see everything and nothing could hide in the gaps.

Underground spaces were worse. The cellar and lower service rooms at my secondary school flooded while I was in Year 11. Classes were moved into temporary buildings during the repairs, and I told everybody I preferred the fresh air.

The truth was that I had tried to go downstairs once. I managed four steps before my legs stopped working, the walls began pressing in and I heard a humming that was probably not real, but might have been.

I never tried again.

Oliver's parents telephoned Uncle Graham twice while we were in sixth form. Their son was no longer coming home most nights. He had abandoned the tennis club, the debating society, his A-level work and the programme of university open days and UCAS preparation they had constructed around his future.

They had found notebooks in his room filled with newspaper cuttings about disappearances near old mine workings throughout the South Wales coalfield, the Forest of Dean, Cornwall and other British mining districts. There were maps overlaid with geological surveys and lists of abandoned levels, shafts and adits cross-referenced against missing-person reports dating back to 1892.

Uncle Graham asked whether I knew what was happening to Oliver.

I said we had drifted apart. It was not entirely a lie.

The humming found me anyway.

The first time was at a building site near Uncle Graham's garage. Contractors were excavating foundations, heavy machinery tearing into ground that had lain untouched for decades. I was walking home from college when I felt that vibration in my chest and the pressure behind my eyes.

It lasted perhaps ten seconds, long enough to blur my sight, make my hands shake and lock every muscle in my body until it stopped.

No one else noticed. The workers continued operating the machinery. Traffic kept moving. The world carried on as though nothing had happened.

It happened again four months later near an old textile mill being converted into warehouse flats. It came again on an underground railway platform during a visit to London for a planning work placement.

It was always near places descending into the earth, places where the ground had been broken, sealed or disturbed. Always the same frequency, the same vibration in my chest and the same sense of wrongness.

I began making annual visits to Idris's land the summer after finishing sixth form. I told no one where I was going. I took two buses and walked the final ten kilometres because I could not yet afford a car and Uncle Graham would have asked questions I could not answer.

Ownership of the smallholding had passed to the local authority after Idris's conviction. He had no other close family, no effective will and nobody willing to assume responsibility for land carrying such a history.

The authority had fixed new NO TRESPASSING signs to the trees every six metres or so, bright orange instead of rusted metal. The chains blocking the side paths remained unchanged.

Undergrowth had reclaimed our campsite beside the stream. It was difficult to see where we had built the fire ring, where we had pitched our tents and where we had felt safe for precisely one night before everything ended.

Oliver was already there when I arrived. He sat near the sealed entrance with his back against a tree. Three empty bottles lay beside him, and he held a fourth.

He had lost weight. Dark rings beneath his eyes matched mine. His clothes no longer fitted properly and looked as though he had slept in them.

He said nothing when I approached. I sat three metres away and left the distance between us.

We remained there until the sun began to set.

I had brought flowers, carnations from a supermarket, nothing special. I placed them near the concrete seal with its official warning notices and steel reinforcement. Oliver watched without moving or speaking. He acknowledged the gesture only with a slight nod that might have been my imagination.

The second year, he brought a notebook. He did not show me its contents. He merely held it against his chest while we occupied our separate spaces and the woods darkened around us.

Neither of us spoke Callum's name aloud. Saying it felt like inviting something back.

In the third year, Oliver's hand shook so badly that he could scarcely light a cigarette. By then I had begun bringing sandwiches. I knew he probably did not eat regular meals, and I knew his parents had finally stopped trying to repair whatever had broken inside him.

He accepted the food without comment. We ate in silence while evening settled into the hollows between the trees.

In the fourth year, he showed me one of his notebooks.

It contained page after page of missing-person reports, all involving people last seen within eight kilometres of abandoned workings. The dates reached back more than a century. He had identified clusters of disappearances every seven to twelve years, usually during the summer and usually involving people aged between fourteen and thirty.

Geological surveys marked unusual mineral deposits. Charts showed underground water tables that did not correspond with the surface landscape. Seismic records showed vibrations without an identifiable source.

I looked at his research and saw an obsession mirroring my own, merely pointed in another direction. Oliver was trying to prove something. I was trying to forget.

Neither of us was succeeding.

The humming continued to find me between our annual visits. It was never predictable and never occurred in the same kind of place twice running: an underground platform in London during a planning placement, the lower level of a multi-storey car park beside my further-education college, the service tunnel connecting two campus buildings.

It always came underground or beside excavated earth. It always had the same frequency. It always lasted just long enough to remind me.

It reminded me that what happened had not been a hallucination born of grief, teenage hysteria or the elaborate lie DI Gareth Vaughan thought we had constructed. The sounds had been real. Callum had run towards something that existed even though it should not. Idris had spent his life keeping people away from whatever moved through those sealed workings.

No one else heard it.

Whenever it began, I watched people's faces for recognition or some sign that the vibration affected them. There was nothing. People walked past, continued their conversations, checked their mobiles and existed in a world that frequency could not penetrate.

There was only me.

And Oliver, judging by the way he sometimes flinched during our annual visits, and by the way his gaze went distant and his breathing changed even when the woods were silent.

Only us, carrying proof that no one else could perceive.

Oliver appeared at my flat on Tuesday, 14 March 2017, ten years after Callum's disappearance. We were both twenty-five.

He looked dreadful. His cheekbones protruded through papery grey skin, and his eyes had sunk so deeply that the surrounding shadows made them appear hollow. He had lost about two stone since I had last seen him four months earlier at the smallholding.

He arrived in a pick-up I did not recognise and parked across two spaces behind Uncle Graham's garage. The engine continued ticking after he switched it off, making the noise of metal pushed too hard for too long.

"I need you to see something."

His voice was rougher than I remembered, scraped raw.

I stood in my doorway with one hand against the frame.

"Whose pick-up is that?"

"It doesn't matter."

He climbed out, went round to the passenger side and retrieved a cardboard box that had been folded and unfolded so often that its corners had become soft.

"Just look at these."

The box held maps, road atlases with pages torn out, topographical surveys printed on ordinary paper and geological assessment documents that looked official enough to have come from council archives, government records or mining-company files.

Every map bore marks. Red crosses clustered across the South Wales coalfield, the Forest of Dean, Cornwall and other mining districts. Some had dates beside them in Oliver's cramped handwriting, reaching back decades.

"I've been tracking it," he said.

He set the box on my kitchen worktop and began spreading the maps across it. His hand trembled.

"The disappearances aren't random. There's a pattern involving mineral deposits, water tables, seismic activity and abandoned workings. It's connected. All of it."

I had heard versions of this during our annual visits to Idris's land, but something was different now. Oliver seemed more desperate and more urgent. His eyes kept darting towards my window and the yard below, checking for something.

"Where did you get the pick-up?"

"I borrowed it from one of the metal thieves. Or one of their mates."

He would not look at me.

"That's how I got involved with them. It doesn't matter. These do."

He took three already opened envelopes from his jacket. They were addressed to Oliver at the front in blocky, slightly unsteady capitals. Inside each was a separate letter bearing my name.

"Idris sent them in my correspondence," Oliver said. "They're for you. He's dying."

"What?"

"Lung cancer. Stage four. They think he has perhaps six months."

I accepted the letters. The return address was a prison in England, several hours away.

"He's been writing to me for two years," Oliver continued. "He's explained things about the level, what his grandfather told him and why the rules existed. There are other places, Aaron. Not only his land. Dozens of them. Perhaps hundreds. Old workings where the ground was opened and something-"

He stopped and pressed both palms against my worktop.

"Just read them. He explains it better."

I put the letters down without opening them.

"Oliver, you need food and sleep. You look-"

"I'm fine."

He swept the maps back into the box, his movements jerky and poorly coordinated.

"I've got somewhere to be. I only wanted you to have those."

He was through the door before I could reply, descending the outside stairs two at a time and climbing back into the pick-up. The engine turned over roughly and backfired once.

He reversed too quickly and nearly struck Uncle Graham's tool trolley. I watched his rear lights disappear towards the main road.

I did not sleep that night. I read each of Idris's letters three times, struggling to extract meaning from sentences that wandered and circled back.

There were references to family stories, old mining methods and warnings that sounded half like folklore and half like technical records. Idris wrote about frequencies travelling through bedrock and certain geological formations behaving like resonators. He wrote about his grandfather's rules and why they mattered.

He never claimed to understand the thing itself. He only knew that it reacted when people noticed or challenged it, that it used voices, and that sealed entrances did not confine it where mining networks and resonant stone continued beneath the land.

The third letter ended with coordinates and a date two days away: 16 March 2017.

"Oliver needs help," Idris had written. "He's become involved with men who don't understand what they're dealing with. If you still care about him, go."

The following morning, I found the location on one of Oliver's maps. It marked abandoned copper workings in Cornwall, including a flooded open working and several unsafe exploratory adits.

The operator had stopped work in the early 1990s after falling metal prices forced it into insolvency. The site had been partially made safe. Some spoil had been moved, erosion barriers had been installed, and then the work had stopped when the money ran out.

By twenty-five, I owned a modest second-hand car. The journey took about six hours.

The access road had deteriorated into gravel and potholes, with weeds forcing their way through the remains of the tarmac. I passed a rusted gate hanging open from broken hinges and continued until the road ended in a clearing enclosed by exposed rock faces and artificial mounds of displaced spoil.

Five vehicles stood there. One was Oliver's borrowed pick-up. Three others belonged to the criminals: two more pick-ups and a van with blacked-out windows. My car made the fifth.

I parked and got out.

Men's voices came from beyond the rock face. Their echoes made them difficult to count.

I found them in an old open working, now partly flooded by water seeping through fractured bedrock. Oliver stood with three men I had never seen. Two carried battery-powered work lamps. The third, evidently the gang's leader, had a coil of rope over one shoulder.

Oliver saw me and went rigid.

"Who's this?" the rope-carrying man asked.

He turned towards me. He was in his forties, with a weathered face and hands scarred by manual labour.

"Nobody," Oliver said quickly. "Just a friend. He's leaving."

"A friend who followed you here?"

The gang's leader studied me.

"Seems interested."

My mouth had gone dry, but I forced the words out.

"I'm looking to buy copper. I heard you might have some."

I knew at once that it was the wrong answer. The three men exchanged glances, and the rope-carrying man smiled without warmth.

"Is that right?"

He stepped closer.

"Funny. Oliver never mentioned having friends in the metal trade."

The men had been using Oliver to explore unstable adits too dangerous for them to enter. They sent him down with a head torch and instructions to identify copper cable and other recoverable metal, mark the positions of support timbers and assess the risk of collapse.

Oliver was expendable: light enough to negotiate narrow passages and desperate enough to accept the danger for whatever they paid him.

I should have left. I should have run.

Instead I continued talking, attempting to convince them that I was a legitimate buyer with cash, contacts and a genuine interest in purchasing whatever they stripped from the workings. Every sentence deepened the lie.

The gang's leader listened, nodded and waited until I had finished.

"Show us your cash, then."

I had about sixty pounds in my wallet.

His smile widened.

"Thought so."

The three men herded Oliver and me into a horizontal adit branching from the flooded open working. It was one of the exploratory passages driven before the operator abandoned the site.

The entrance was only about one and a half metres high. Rotting timbers supported it, bowing beneath the weight of the earth above. I had to duck to enter and force my legs to keep moving while my chest tightened and my vision narrowed at the edges.

Six metres inside, the passage widened slightly into a rough chamber. The men positioned us against the far wall and aimed their work lamps into our faces, preventing us from seeing more than silhouettes beyond the glare.

"The problem is," the rope-carrying man said in an easy, conversational voice, "you two know where we're working now. You know what we're taking out. That makes you a liability."

Oliver wrapped his arms around himself and breathed too quickly.

"We haven't seen anything," I said. "We'll leave. We won't tell anyone."

"Of course you won't."

The gang's leader sounded almost sympathetic.

"But we can't really take that chance, can we?"

One of the other men moved behind us, blocking the tunnel exit. They discussed the practicalities: how deep into the workings they should take us, whether to bring down part of the adit or simply leave us in a section that would flood when the groundwater rose after heavy rain. They wondered how long it would be before anyone thought to search there, and whether it mattered. They spoke in the same tone people used to discuss where to eat or what to do at the weekend.

I understood then, properly understood, that we were going to die there. These men had done this before, or something close enough to it, and they would do it again. Oliver and I would disappear into that maze of workings and nobody would find us. Nobody would ever know.

Just as Callum had disappeared into the coal workings on Idris's land ten years earlier.

My back pressed against damp stone. Somewhere farther inside the mine, water dripped with a steady percussion in the darkness beyond the work lamps.

Oliver was no longer breathing quickly. His shoulders had gone slack, the posture of someone who had stopped fighting. I had spent ten years avoiding underground spaces, remote countryside and anything that reminded me of that night at Idris Morgan's smallholding. Now I was going to die in exactly the sort of place I had built my entire adult life around escaping.

The men were still talking, still deciding. One of them checked his watch.

Then the humming began.

It was a low frequency, barely audible at first. I felt it as a vibration in the stone against my spine and in the ground beneath my boots. It built steadily until it filled my chest, my jaw and the space behind my eyes. It followed the same pulse I had not heard this strongly since the night Callum vanished: three seconds on, one second off.

The work lamps flickered.

The man guarding the exit dropped his torch first. It struck the tunnel floor with a crack that echoed from the wet stone. Its beam spun wildly over the ceiling before settling at an angle that illuminated his boots. He stood frozen for perhaps three seconds while the humming grew from something barely perceptible into a vibration deep within the bones.

Three on, one off.

Three on, one off.

Then he ran. He said nothing to the other two and did not stop for his equipment. He simply turned and bolted towards the flooded open working.

His footsteps hammered against the packed earth. His breathing came in harsh gasps that rebounded from the tunnel walls long after he disappeared around the bend.

The remaining men looked at each other. The man with the work lamp still held it towards Oliver's face, but his hand had begun to shake so badly that shadows jerked across the walls. The rope-carrying man, the gang's leader, had gone completely still. His head was tilted towards the sound.

"What the fuck is that?" the man with the lamp asked. His voice came out thin and high.

The humming shifted lower. It sank into a frequency that filled my chest cavity and jaw, making my teeth ache and blurring the edges of my sight. The work lamps flickered once, then twice, before settling into a dimmer glow that turned everything the colour of old bruises.

The gang's leader dropped his coil of rope. It landed in a puddle with a wet slap.

"We need to go," he said quietly, almost conversationally, although his feet were already carrying him backwards towards the exit. "We need to go right fucking now."

The man with the lamp began to argue. He managed perhaps two words before the humming dropped again and something in the tunnel changed.

The air pressure shifted, making my ears pop. Suddenly I could smell mineral deposits, stagnant water and something beneath them that carried me back to Idris's land: sitting on the cottage porch at dawn, exactly where Idris had ordered us to remain, listening to a perfect imitation of Callum's voice calling for help from the sealed coal level.

Both men ran.

They left their work lamps behind. One lay on the ground and the other rested against the tunnel wall where it had fallen, both still shining weakly.

Their footsteps echoed towards the open working for perhaps ten seconds, overlapping with the pulse, and then changed as they reached the larger chamber beyond. The humming surrounded Oliver and me. It came from the walls, floor and ceiling at once, passing through the rotting timber supports, the loose rock and every part of my skeleton.

I waited for panic to take me. I waited for my throat to close and my legs to stop working, as they had whenever I tried to go underground during the previous ten years.

It did not happen.

The frequency wrapped itself around Oliver and me, but it felt different from the humming on Idris's land. That had been angry and relentless, drawing Callum towards the eastern ridge no matter how desperately he ran. This felt almost aware. It was present and watchful. It was not threatening us specifically, but it was hunting something.

A man screamed from deeper within the mine complex.

The sound came through a different passage, perhaps forty-five metres away by the connecting workings. It was high and raw with genuine terror, the sort of scream that meant events had passed beyond reason.

It stopped in the middle of a breath.

Running footsteps pounded through the darkness. Two separate sets at first, fast and panicked, splitting somewhere beyond our sight. One set grew louder, approaching our tunnel through a connecting adit I had not noticed before.

The runner's breathing echoed ahead of him, ragged and desperate.

The humming pulsed harder.

Three on, one off.

Three on, one off.

The approaching footsteps stopped.

There was silence for perhaps five heartbeats. Then came a sound I could not identify, wet and heavy and final. It might have been a body striking stone, or stone striking a body. Either way, it was the kind of impact that left no room for recovery.

Oliver made a low noise in his throat. His shoulders had gone rigid against the tunnel wall, and both hands were pressed flat against the wet rock beside him.

The lamp on the ground lit his face from below, turning his eye sockets black and his skin to wax.

"It knows we're here," he whispered. "It knows we're here, and it's not... It's not taking us."

Another scream came from farther away, near the main entrance and the parked vehicles. It was the third man's voice. I could not distinguish the words, only pleading or swearing or both. Then that voice, too, fell silent.

The humming changed pitch again. It rose almost into the range of speech, forming sounds that were not quite syllables but nevertheless felt deliberate.

The lamps dimmed until we sat in near darkness, with just enough light to see the tunnel walls closing around us and the support timbers sagging overhead.

I tried to stand. I got my legs beneath me and braced one hand against the wall, but my knees gave way and I slid back down beside Oliver. My chest felt hollow. My hands were shaking so badly that I pushed them beneath my thighs to hold them still.

"We should run."

I did not recognise my own voice.

"We should. We need to get out."

"Where?" Oliver had not moved. "Where the fuck would we go?"

He had a point. The tunnel ran roughly six metres back to the open working. Beyond that lay an unknown distance of flooded chambers, exploratory adits and unstable shafts before we could reach daylight.

Whatever was hunting the men who had brought us there stood between us and the exit.

A final cry rose from the direction of the entrance. It lasted longer than the others, rising and falling with the pulse until it seemed to merge with the humming rather than remain a separate sound.

Then everything stopped.

There was complete silence apart from water dripping somewhere in the workings and the residual ringing in my ears. The humming had gone. The work lamp remained dim but steady, no longer flickering. It cast just enough light for me to see the walls, Oliver's profile and the abandoned rope lying in its puddle.

I do not remember deciding to close my eyes. I do not remember my body giving up or my mind shutting down. At some point, however, the terror, exhaustion and ten years spent fleeing underground spaces reached me all at once, and the darkness became larger than the tunnel around us.

I woke beneath fluorescent lights.

There were ceiling tiles stained by old leaks and an antiseptic smell mingling with floor polish and something that might have come from the hospital canteen. I blinked against the brightness until the shapes resolved into a hospital room in an NHS district general hospital in Cornwall.

The bed had rails. A monitor beeped steadily beside me. A bag of clear fluid hung from an intravenous stand, its line connected to my left arm.

My throat felt as though I had swallowed ground glass, and my head pounded in time with my pulse.

Oliver lay in the other bed. I could not tell whether he was asleep or unconscious. His face looked even worse under the fluorescent lights than it had in the borrowed pick-up: grey skin stretched tightly over bone, with dark circles beneath his eyes so deep they looked painted on.

A man sat in the chair between our beds. He appeared to be in his mid-forties, with an athletic build and close-cropped black hair greying at the temples. He wore an open-collar shirt and dark trousers, with no uniform or tie, but something in the way he sat made it obvious that he was police.

"You're awake," he said. He did not smile. "I'm Detective Chief Inspector Daniel Rees. I've been seconded to a national missing-persons inquiry involving former mining districts. The local force contacted me when they found you and your friend in those workings."

My mouth was too dry to answer. He noticed, poured water from a plastic jug into a cup and handed it to me.

I drank half before my throat loosened enough for speech.

"How long?"

"Thirty-six hours." Rees leant back and watched my face. "Mine-rescue specialists brought you both out yesterday morning. You were unconscious, dehydrated and hypothermic. Your friend suffered a seizure in the ambulance, but he's stable now. Neither of you has traumatic injuries."

"The others." The words scraped from my throat. "The men who brought us there."

"Gone," Rees said. His expression did not change. "We found their vehicles and equipment, but we didn't find them."

He allowed the words to settle while I tried to absorb them. The monitor continued beeping. Oliver's breathing remained shallow but steady.

"How did anyone find us?"

"The site is checked intermittently because of reports of illegal metal theft. One of the men's associates became concerned when nobody returned and anonymously reported the vehicles. A patrol confirmed that three vehicles belonging to the gang were at the site, along with the borrowed pick-up your friend drove there and your car. That gave the local police a reason to send in a specialist team."

Rees took a small notebook from his pocket and turned through several pages.

"I remembered your name from the reports," he said, touching one page. "Callum Morgan disappeared on 21 July 2006, near his grandfather's smallholding. You and Oliver Shaw were the last people known to have seen him alive."

I placed the cup on the bedside table. My hand shook hard enough to make it rattle against the plastic.

"Idris Morgan was convicted of Callum's murder," Rees continued. "He's serving a life sentence in a prison in England, with a minimum term of fifteen years. He's still alive, but he's in the prison infirmary with lung cancer."

My fingers tightened around the edge of the mattress.

"I read the original reports when I was a young detective," Rees said. "The case later became relevant to the cross-force inquiry I'm working on. I never accepted the prosecution's version."

He closed the notebook.

"Too many details didn't fit. His warnings about the coal level were presented as threats. Gaps and changes in his search account were attributed to his knowledge of the land, rather than his age, poor hearing and exhaustion. The Crown alleged an unobserved confrontation with Callum, but there was no body and no reliable forensic evidence of one. An overworked junior legal-aid barrister did what he could, but the Crown prosecutor built a persuasive circumstantial case around Idris's temper, his knowledge of dangerous mines and the inconsistencies in his interviews. It should not have been enough. Somehow, it was."

"You believe us," I said. It was not a question.

"I believe you saw something that night which you couldn't explain. I believe Callum Morgan vanished without a trace despite specialist search teams, mountain rescue volunteers and police dogs covering that land. I believe the survey crews used ground-penetrating radar, thermal imaging and borehole cameras without finding any route he could have taken beyond the sealed entrance."

Rees returned the notebook to his pocket.

"I also believe that whatever happened in those copper workings two nights ago will not appear in any official report."

The monitor kept beeping. Oliver stirred but did not wake.

"The men who took you there had records for assault and theft," Rees said. "Two had outstanding arrest warrants. They were stripping copper cable and recoverable metal from abandoned workings. When they fail to turn up, the investigation will proceed, but there may be very little to find. Collapses happen. Flooded shafts and unsafe adits kill people."

He stood and walked to the window, looking out over the hospital car park.

"But you and your friend were found without traumatic injuries. You were dehydrated and hypothermic, and Oliver had a seizure, yet neither of you had so much as a broken bone."

He turned towards me.

"This is what happens next. You recover. You are discharged. Then you leave. Not merely this hospital or Cornwall. Leave the mining districts entirely. Go somewhere else and stay there."

His voice remained level, but his eyes had hardened.

"Whatever is in those old workings, whatever took Callum Morgan and those three men, has allowed you to walk away twice. Idris's warnings gave you an earlier chance that you ignored. I would not rely on being given another. The same advice applies to Oliver. He has family, money and resources. He should use them somewhere far from here."

Rees took a business card from his wallet and placed it on my bedside table.

"If either of you needs to talk about what happened, ring that number. It leads to a voicemail I check once a week. But don't come back here. Don't approach abandoned mines. Don't test your luck."

He walked towards the door, then stopped with one hand on the frame.

"Idris Morgan has spent ten years in prison for a crime I don't believe he committed. Callum is still missing. Those three men are gone, and we may never receive a formal missing-person report for any of them."

He met my eyes.

"You got out. Stay out."

The door closed behind him with a soft click.

I lay listening to the monitor, Oliver's breathing and the voices passing in the corridor. Fluid dripped steadily through my intravenous line. The water stains on the ceiling formed patterns that looked almost deliberate.

Rees's card rested where he had left it, plain white with a telephone number and nothing else.

I closed my eyes and saw the tunnel walls pressing in. I felt the humming in my chest and heard screams ending halfway through a breath.

We would leave as soon as the hospital discharged us and Oliver could walk. We would go east until the hills disappeared behind us and the ground felt solid beneath our feet.

Whatever had been down there had let us go. I would not give it a reason to change its mind.

We left three days after our discharge. We did not discuss the decision or debate destinations. Oliver returned the borrowed pick-up to the associate from whom he had taken it, a man connected to the metal thieves, and we loaded everything we intended to keep into my modest second-hand car.

There were two holdalls, a box containing Oliver's notebooks that he could not bring himself to burn, my laptop and Uncle Graham's old camping pans, which I had never returned.

We drove east across England. As the Welsh hills and the higher ground of the west receded behind us, the horizon opened. We kept going until we reached Norwich, where the countryside lay comparatively flat and no ridge enclosed the city.

Norwich was less a choice than the place where we finally ran out of momentum. Its visible horizons, orderly streets and low Norfolk skyline felt like the opposite of every valley and wooded hillside we had fled.

We found a two-bedroom fourth-floor flat above shops near a launderette and a Vietnamese cafe on Dereham Road. Its east-facing windows caught the morning light across a carpet worn so thin that the routes between the rooms showed through to the backing. The rent was GBP 850 per month, divided between us. There was a bus stop nearby and a Tesco Express visible from the kitchen window.

Within six weeks I found a junior development-management post in the local council's planning department. The qualification I had earned through further-education study and a part-time planning course, after years of borrowing town-planning and transport-design books from the library, was finally useful. I reviewed planning applications, checked proposals against local policy and flagged breaches or missing information. The pay covered my share of the rent and the food.

Oliver found night shifts at a distribution warehouse the size of several football pitches. He loaded articulated lorries and managed stock in a building where everything remained visible beneath high-bay LED lighting and nothing went underground except the surface-water drains.

The humming stopped.

I first noticed its absence perhaps two months after we had settled in Norwich. I was waiting for a local train and felt the familiar tightness begin in my chest. On the approach to the city, the line entered a covered cutting and a short tunnel. I waited for the vibration in my jaw and the pressure behind my eyes.

Nothing came.

The train entered the darkness and emerged again into daylight. I made the journey back and forth three times that afternoon, holding my breath each time the windows went black.

There was only silence beneath the mechanical rattle of wheels on rails, the pneumatic hiss of the doors and announcements crackling from overhead speakers.

I tested the absence elsewhere. I could not help myself.

I walked to the lowest level of a multi-storey car park and stood for twenty minutes among concrete pillars, painted bays and oil stains. I visited construction sites where foundations had been excavated and new buildings had broken the ground. During work placements in London, I forced myself to stand on underground railway platforms. I crossed a pedestrian subway beneath the Norwich ring road while articulated lorries thundered overhead and pigeons nested on the beams.

Nothing.

Whatever frequency had followed me for ten years, finding me in car parks, stations and every place where the earth had been disturbed, enclosed or broken, had released me.

Oliver never said whether he could still hear it. We discussed very little during our first eight months in the flat.

We lived parallel lives, passing in the narrow kitchen and nodding when our shifts overlapped. He worked nights and slept during the day behind blackout curtains. I kept ordinary office hours and usually came home to find him gone or preparing to leave.

But we were both there. That mattered.

The nightmares began in the third month for both of us.

I woke choking, convinced that the ceiling had dropped to one and a half metres and that rotting timbers stood above me while soil sifted through the gaps. Oliver's nightmares came with screaming - not his own, but the cries the men had made before the humming took them.

I heard him thrashing in bed through the wall. I would get up and stand outside his door without knocking, waiting until the sounds stopped and his breathing settled.

He did the same for me. I would surface from whatever dark shaft my mind had dragged me into and find his shadow in my doorway. Neither of us spoke during those moments. He remained there for perhaps five minutes, then returned to his room or went to the kitchen if his shift was about to begin.

The panic attacks were worse and less predictable.

Mine were still triggered by confined spaces. A cramped records cupboard at work sent me into a spiral that lasted forty minutes. I locked myself in a lavatory cubicle and tried to remember how to breathe. Cellars, service tunnels and underground plant rooms remained impossible.

Oliver's attacks came from sound: construction machinery, heavy equipment and anything that produced a low mechanical hum.

Once, I found him frozen on the pavement outside our building, staring at a pneumatic drill breaking the road open for a water-main repair. He stood motionless until I touched his elbow. Then he blinked and carried on walking without acknowledging what had happened.

We began eating dinner together around the ninth month.

There was nothing formal about it. I cooked rice with whatever meat or other protein was cheapest. Oliver came to the table if his shift did not begin until ten. We sat opposite each other with plates and forks while the television played news that neither of us watched.

The first few times, we did not exchange a word. There was only the sound of cutlery, the traffic on Dereham Road and somebody's music through the wall.

Then, one evening, Oliver asked, "Do you still check the cellar doors and service stairs?"

"Yes," I said.

He nodded, and that was enough.

Small conversations grew from there: complaints about work, the weather, whether the Vietnamese cafe downstairs was worth trying, and whether its food-hygiene rating ought to concern us. Ordinary things. The kind of conversation people who had not spent ten years haunted by frequencies in the bedrock could have without a second thought.

I never returned to South Wales. I did not visit Idris in prison, even after Rees told me how ill he was.

Eight months after Oliver and I moved to Norwich, Rees rang to say that Idris had died in the prison infirmary. Lung cancer. There would be no public service.

I ended the call and stood in our kitchen, looking through the window at the distant, low Norfolk horizon, where no ridge enclosed the view.

Idris had spent the last ten years of his life imprisoned for a murder he had not committed, while his grandson remained trapped somewhere beneath his own land, or beneath places connected to it in ways I could not understand.

I should have visited him. I should have made the journey to England sooner and sat opposite him in whatever visiting room the prison allowed. I should have told him that I believed him and knew he was not responsible. I should have said that Callum had made his own choice when he ran towards the eastern ridge, unless the humming had made the choice for him.

But I had not gone.

I could not force myself back towards the Welsh hills or anywhere that old workings passed unseen beneath the ground, even for Idris.

Oliver and I stopped making our annual visits as well. There were no more supermarket carnations at the coal-level entrance, no more sitting three metres apart near the sealed opening where Callum had disappeared.

Ownership of the smallholding had passed to the local authority after Idris's conviction. There was probably new fencing by then. Perhaps one day the land would be sold to developers who would never know what it had taken, or that sealing the recorded entrance had never silenced the inaccessible workings beneath it.

I still thought about Callum, mostly at night while I lay in bed listening to the constant murmur of Norwich traffic.

I wondered whether some part of him remained down there. I wondered whether the presence in the workings had kept him, consumed him or changed him into something else. I wondered whether he had truly wanted to run that night, or whether the frequency had drawn him as it later drew the three men through the Cornish mine before hunting them.

I did not need the answers.

I did not need to understand why it had taken Callum but allowed Oliver and me to walk away twice. I did not need to know why it killed three men who had intended to murder us but spared two boys who had ignored every warning they were given.

That did not make it merciful, benevolent or just. Whatever intelligence, force or ancient presence moved through resonant stone and abandoned workings had made a choice. I had no reason to believe its choices followed any morality I could recognise.

It had taken Callum ten years earlier. It had allowed Oliver and me to survive when we should have died beside the metal thieves. It had released us from the copper workings without broken bones or visible wounds, though it left us dehydrated, hypothermic and changed in ways no hospital examination could record.

I would not question our escape by going near another abandoned mine.

Idris's warning had been our first chance to turn away. Surviving the night Callum vanished had been our first escape. Leaving Cornwall alive had been our second.

Whatever hummed beneath the hills had finally let us go, and the only sensible response was to remain gone.