The Tapping in the Walls

I've spent the last four years crawling through cellars for Scottish and Southern Electricity Networks, working on the local electricity distribution network, so strange smells don't bother me much any more. Wet concrete, old insulation that's been rotting since the eighties, that particular sort of mouse problem which tells you you'll find something dead within the next ten minutes. You deal with it and carry on working.

That ought to have prepared me better for what happened with Jamie.

It didn't.

Dad died in March. Martin Price had a heart attack at a local ironmonger's on a Thursday morning. He was gone before the ambulance arrived.

Mum took it hard, obviously, but she became practical very quickly. The terraced house in Southsea had been in the family for twenty-eight years, but there were still several years left on the mortgage and she didn't want to stay there alone. Jamie had been renting a bedsit near the University Quarter by Guildhall Walk. It cost too much and looked smaller every time I visited. I had my own place in Fratton. Nothing special, but it did the job.

Mum found the maisonette listing on a Wednesday. It was the upper part of a divided Victorian house in Eastney, close to Bransbury Park and the seafront, with three bedrooms and rent we could manage if we split it. She asked whether I'd move in with her and Jamie for a while.

"Just until things settle," she said.

"Yeah. All right."

We moved in during April. The maisonette was older than it had looked in the photographs, which was fairly standard. Painted floorboards creaked in particular places, the windows never quite sealed and the old cast-iron radiators clanked whenever the heating came on. The kitchen had vinyl flooring that curled slightly beside the units.

The conversion had left odd spaces in the building. Boxed-in pipework ran along the landing, and the landlord mentioned an enlarged service void behind the bathroom and Jamie's bedroom, connecting with a crawl space beneath the ground floor. It was supposed to give access to old plumbing and electrical runs, though the access panels had been sealed years before. At the time, it was just another bit of awkward Victorian building work.

The ground-floor flat was occupied by a couple in their fifties who kept themselves to themselves and didn't care what we did as long as we kept the noise down after ten.

I took the larger bedroom because Jamie didn't want it. He chose the small room at the end of the landing, beside the bathroom. There was barely enough space for a single bed and a desk. Mum had the main bedroom with its little en suite, which made sense.

Jamie kept to himself. That wasn't new. He was my younger brother and had always been quieter than me, more inclined to disappear into his own thoughts. After Dad died, it became worse.

He would come home from his part-time job at the University of Portsmouth Students' Union shop, go straight to his room and stay there until he needed food or had to leave again. Mum worried. That wasn't new either. I thought he needed time.

Then the trips began.

The first was on a Saturday in May. Jamie got up early, said very little, went down to the Portsmouth passenger-ferry terminal and crossed to Ryde. He spent the day on the Isle of Wight and returned after dark.

He went straight to his room. Mum asked where he'd been. He said he'd wanted to walk around.

Fine. Odd, but not impossible.

The following weekend he did it again. The same early ferry to Ryde, the whole day gone, then home after dark.

On the third weekend he went farther. He caught island buses across to Yarmouth and didn't return until nearly midnight. Mum was pacing the kitchen when I got home from Dan Mercer's place.

"Do you think Jamie's all right?" she asked.

"Probably."

She didn't look convinced.

The fourth trip was when the photographs began. Jamie went back towards Yarmouth, this time travelling on to Fort Victoria Country Park. I didn't know much about it beyond the fact that the site had old coastal fortifications overlooking the Solent.

There were concrete emplacements, remnants of gun batteries and sealed sections left from the old defences. Jamie sent Mum a photograph of a concrete doorway with rusted hinges still attached. Then another showing the entrance to a passage with a metal barrier across it.

The third showed a sealed hatch set into the ground.

Mum showed me the photographs on her mobile and asked what I thought he was doing there.

"He probably likes the history," I said. "Exploring old structures. Plenty of people are interested in that."

She scrolled back through the pictures.

"He's been going every weekend for a month."

I looked again. The doorways were dark. Moss grew around the passage entrance. The hatch looked as though it hadn't been opened in decades.

I told her I'd speak to him.

I didn't get round to it. Work became busy. We had a substation refurbishment in Cosham that overran, and I was covering extra shifts for a bloke on leave.

I'd get home late, eat something and collapse into bed. Jamie was usually already in his room. Mum kept showing me photographs. More fortifications. More sealed doors.

One showed black, motionless water pooled before an opening. Another showed faded graffiti across old concrete walls.

"Has he said why he keeps going back?" I asked.

"No. He just sends the pictures."

That was all.

Then came Friday, 9 June 2023. I remember the date because I'd planned to take the weekend off and sleep properly for once. I got home at about six. Mum was in the kitchen making supper.

"Is Jamie home yet?" I asked.

"No. He texted this morning. He said he was going to Yarmouth again, then out to the fort."

I took a bottle of lager from the fridge and sat at the table.

"Did he say when he'd be back?"

She shook her head.

"He normally makes it back before midnight," she said.

"All right."

Midnight came and went. Mum texted him.

"No answer."

Her calls went straight to voicemail. By one in the morning she was standing in my doorway, asking whether I thought we should call someone. I sat up and checked my own mobile. Nothing from Jamie.

I sent him a message. It didn't deliver.

"Maybe his phone's died," Mum said.

"Probably."

She remained in the doorway, holding her mobile in both hands. Then she asked if I could drive into the University Quarter and check his usual places. Perhaps he'd gone back towards the university instead of coming home.

"It's one in the morning. Everything will be dead."

"Please, Callum."

So I dressed and drove over. It took about twenty minutes. I parked near the Students' Union shop and walked around. There was no sign of him.

I checked the cafe he liked on Guildhall Walk. Closed. I passed his old bedsit. The lights were out.

I texted Mum and told her he wasn't there. She rang me almost at once.

"Can you check the library?"

"It'll be locked."

"Just try."

I walked to the University of Portsmouth Library. It was locked. I went round the entire building.

"Nothing," I said when I called her back. "I'm coming home."

She sounded as though she'd been crying.

I reached the maisonette at around half past two. Mum was still awake, sitting on the sofa with her mobile in her lap.

She asked whether we should report Jamie missing. I said we ought to wait until morning. He was an adult. He had probably missed the final bus connection to Ryde, then the last ferry, and found somewhere to spend the night.

She said nothing. I sat beside her and we waited.

At 02:53, on Saturday, 10 June, her mobile buzzed.

She snatched it up so quickly she nearly dropped it. She opened the message and stared. I leaned over.

It was from Jamie.

A photograph. Blurred, dark and difficult to understand. There was water, perhaps, black and flat. Across the top lay a thin line of lighter grey that might have been sky, fog or nothing at all.

The location data placed it near Hurst Point, across the Solent from the western end of the island. That was close enough to the coast around Fort Victoria to be possible, but not where he had told us he was exploring.

Below the photograph, he'd written: "I'm fine. Phone's dying."

Mum released a long breath and replied immediately.

"Where are you? Do you need a lift?"

There was no response. Her call went straight to voicemail.

"At least he's all right," she said.

I took her mobile and enlarged the photograph. The water was too dark to show any detail. There was something in the lower-left corner, though. A grey smear, out of focus and too close to the lens to belong to the background.

I assumed it was the edge of Jamie's rucksack strap. I zoomed in, but the shape only grew larger, never clearer. It was a textured grey mass pressed against the edge of the frame.

Mum asked what I was studying. I didn't answer at first.

The angle seemed wrong. The shape looked too close, too immediate, as though it were leaning towards the camera rather than merely caught beside it.

"Callum?"

I handed back her mobile.

"Did you see something?"

"No. It's just a strange photograph."

She examined it again.

"He was probably tired."

"Probably. Took a bad picture in the dark."

She went to bed a few minutes later. I stayed on the sofa and opened my own message thread with Jamie. His last message to me had been three weeks earlier, a thumbs-up in answer to a question about washing-up liquid.

I considered messaging him again. I didn't.

Mum had forwarded the photograph while we sat there. I enlarged the grey smear again. It still looked wrong. I couldn't stop looking at it.

Jamie walked through the door on Sunday afternoon, 11 June.

I was on the sofa watching something I hadn't been following. Mum was in the kitchen, wiping worktops she'd already cleaned twice. The lock clicked. She dropped the sponge and almost ran into the hall.

Jamie came in carrying his rucksack and looking completely normal.

That was the strange part. He looked fine.

Mum seized him and began crying into his shoulder. He stood there and allowed it. He didn't exactly embrace her, but he didn't pull away.

I got up and went over. That was when I noticed his hair. It wasn't damp. It was wet, as if he'd just stepped out of a shower or walked through heavy rain.

It hadn't rained. I'd checked the forecast three times that morning because I intended to drive to the ferry terminal and start looking for him if he wasn't home by four. It had been 14 degrees Celsius and dry, with clear spells all weekend.

His hair was soaked.

Mum drew back and held his face between her hands.

"Where were you? Why didn't you call? I was about to ring the police, Jamie. I was this close."

"My phone died."

His voice sounded normal as well. Quiet, but normal. That was Jamie.

"You've been gone since yesterday morning," Mum said. "It's nearly three. Where did you sleep?"

"At the park. There are benches."

Mum's expression changed in a way I didn't like. She looked at me, and I looked at Jamie. His rucksack hung from one shoulder. It seemed wrong too. Far too light. The strap wasn't pulling against his hoodie at all.

"What about your charger?" I asked. "You always take your power bank."

Jamie blinked.

"I forgot it."

Mum steered him towards the kitchen.

"Sit down. I'll get you something. Are you hungry? You must be starving."

"I'm all right."

"Sit," Mum said. It wasn't a suggestion.

Jamie sat at the table and let the rucksack slide to the vinyl floor. It landed with almost no sound.

I stood in the doorway while Mum opened the fridge and took out containers. His hoodie was damp as well. Not only around the shoulders. The whole thing.

And it smelt.

Not of sweat. More like seaweed left in the sun, or stagnant salt water trapped between rocks.

Mum put a plate of leftover cottage pie and peas in front of him. Jamie picked up his fork and began eating.

That was when it became strange.

He ate quickly. Far too quickly. He barely chewed, just shovelled food into his mouth, swallowed and took more. His jaw moved, but the motion looked wrong. Too rapid.

The cottage pie was gone in less than a minute, and then he scraped up the peas. Mum watched with one hand covering her mouth. I could tell she wanted to say something but couldn't decide what.

Jamie finished, set down his fork and wiped his mouth with the back of his hand.

"Better?" Mum asked.

"Yeah."

"Where exactly were you?" I asked.

Jamie looked at me. His eyes were red at the edges. Tiredness, perhaps. Or something else.

"Fort Victoria."

"We know that part. You texted Mum before you left."

"I found a passage."

Mum pulled out the chair opposite and sat.

"What passage?"

"Under the old fortifications. There's one that isn't on the maps. It goes farther than the others."

I leaned against the door frame.

"How far?"

"I don't know. I kept walking and it kept going. I thought it would loop back, but it didn't."

"So you got lost," Mum said.

Jamie nodded.

"I got turned around."

"In a tunnel? For an entire day?"

"I didn't have my phone out. I couldn't see the time."

That part almost made sense. The hidden passage he described wasn't one of the recognised public areas of the fort. If he'd found an unmapped, sealed section without proper lighting and gone inside, he could have lost all sense of time.

I'd worked in cellars like that. Once you'd been underground long enough, your sense of direction began to fail.

"You should have stayed put," Mum said. "If you're lost, you're meant to remain in one place."

"I wasn't lost," Jamie said. "I was just turned around."

Mum rubbed her face. She looked exhausted. I doubted she'd slept.

"Don't do that again," she said. "Please. I can't go through that again."

"Okay."

Jamie stood and picked up his rucksack. It lifted much too easily. He passed me, went down the landing and closed his bedroom door.

Mum stared at me.

"That's it?"

"What do you want him to say?"

"I don't know. Something. An apology, perhaps."

"He said all right."

"That isn't an apology."

I sat in the chair Jamie had left. The seat was still warm.

"He's fine. He became lost in a passage, missed the last connection and had to stay overnight. It happens."

"His hair was wet."

"He probably splashed water over his face in a public loo somewhere."

Mum didn't look convinced, but she didn't argue. She took Jamie's plate to the sink.

I remained at the table. I wanted to believe what I'd said. It was a reasonable explanation. Jamie had gone exploring, lost track of time, become stranded overnight and come home. Simple.

But the lightness of his rucksack bothered me.

So did the smell.

I went to my room. I assumed the whole thing would blow over by the next day. Mum would calm down. Jamie would return to his usual routine. We'd all pretend it hadn't happened.

That was what I wanted.

At about eleven that night, Mum knocked on my door. I was already half asleep. When I opened it, she stood there in her dressing gown with her arms folded.

"Can you smell that?"

I sniffed.

"Yeah."

It was sour. I'd noticed it faintly around the maisonette for a week or so, but now it was stronger.

"Smells as though something's died in the walls," I said.

"It's getting worse. I can't sleep with it."

I sighed and pulled on a shirt.

"I'll check the pipes."

Mum followed me to the kitchen. I knelt, opened the cupboard beneath the sink and removed the cleaning supplies and bin bags. Using my mobile's torch, I examined the pipework at the back. It looked fine. No leaks. No standing water. The trap was clean.

I checked beneath the bathroom basin as well. Nothing.

The smell remained, thick and low. It reminded me of the mud near the ferry terminal when the tide was out, rotting weed mixed with wet silt.

"I can't see anything," I said.

Mum stood on the landing, hugging herself.

"Perhaps it's the heating. Something trapped near a radiator or in the vents."

"Perhaps."

I didn't think so. The smell wasn't coming from one place. It was everywhere.

I walked along the landing towards my room and passed Jamie's door. It was closed, but light showed beneath it. I stopped. I don't know why. I had a feeling.

I knocked.

"Jamie?"

There was no answer. I opened the door.

Jamie lay on the floor beside his bed, his ear pressed against one of the cold cast-iron heating pipes. He wasn't moving.

"What are you doing?"

He didn't look towards me.

"Listening."

"To what?"

"The pipes. They tap."

I stepped inside. The smell was much worse in his room. The low-tide stink was so dense I nearly backed out.

"Heating pipes tap. That's normal."

"Not like this."

I crouched beside him. The radiator and its pipes had been painted white years ago. The metal was cold beneath my hand. Nobody ran the heating in June.

"It's off."

"I know."

"Then what can you hear?"

Jamie closed his eyes.

"Patterns."

I waited.

"Four taps," he said. "Then it stops. Two taps. Stops again. Then four."

I kept my palm against the pipe. I felt nothing.

"You're tired. You were gone all weekend. You need sleep."

"It's tapping back."

"What?"

"I tapped on it earlier. It answered."

I stood, my knees cracking. I looked down at my younger brother lying on the floor in his damp hoodie, eyes closed and ear pressed to a cold pipe.

"Get some sleep."

I left and shut the door. Mum was waiting on the landing.

"Is he all right?"

"He's fine. Just exhausted."

"What was he doing?"

"Nothing. Go to bed."

She looked at Jamie's door for a long time, then went to her room.

I returned to mine and lay staring at the ceiling. Jamie was tired. It made sense. He'd wandered through the old fortifications for God knew how long without food or proper sleep.

People became strange when they were exhausted. I'd seen it on jobs. Men working double shifts started seeing or hearing things that weren't there.

That was all it was.

But I kept thinking about his rucksack and how light it had been. His hair had still been wet hours after he came home.

And the smell had reached my room. Faint, but present. A sour, rotting odour, like something dragged from deep water and left to decay.

I rolled over, pulled up the duvet and tried not to think about it.

The smell didn't go away.

The week after Jamie returned went wrong from the beginning.

On Monday, 12 June, he didn't go to work. At about eight in the morning, I heard Mum knock on his door.

"Are you awake?"

"Yeah."

"Do you need a lift to the university?"

"No. I'm not going in."

She stood outside his room without speaking, then returned to the kitchen. I was eating cereal. She looked at me and I shrugged.

People missed work. It happened.

On Tuesday, 13 June, I had an early call for a transformer inspection in Portchester. I left the house at about six and didn't return until nearly eight that evening.

The maisonette was quiet. Mum was on the sofa with her laptop, doing finance work for Queen Alexandra Hospital from home.

"Is Jamie here?" I asked.

"Yes. In his room."

"Did he go to work?"

"No."

I went along the landing and knocked.

"Come in," Jamie said.

He was sitting on his bed with his back against the wall, fully dressed in jeans, hoodie and trainers. His desk lamp was off. Only the harsh ceiling light was on.

He looked at me without speaking.

"Are you feeling all right?"

"Yeah."

"Are you planning to go back to work?"

"Probably."

That was all. I closed the door.

On Wednesday, 14 June, I came home at about six and found Mum in the kitchen. She was cutting vegetables but not cooking them. She'd arranged them in neat, even rows across the chopping board.

"What's wrong?"

"Jamie's been in and out all day."

"What do you mean, in and out?"

"He leaves his room and walks into the bathroom or the kitchen. Then he stands there for a few minutes and goes back. Sometimes he leaves the house. He's gone for an hour, then comes straight back to his room."

I took a bottle of lager from the fridge and sat at the table.

"Have you spoken to him?"

"I've tried. He barely says anything."

"Give him space. People deal with grief differently."

She put down the knife and looked at me.

"This isn't dealing with grief. This is something else."

I had no answer.

That night, I woke at about two because I heard footsteps on the landing. They were slow and uneven.

I opened my door. Jamie stood outside the bathroom in the darkness, facing the section of wall where the ventilation grille was fitted.

He wasn't moving. He simply stared at it.

"Jamie."

He turned his head but didn't look at me. His gaze passed beyond me. Then he walked back to his room.

I stood there for a minute before returning to bed.

On Thursday, 15 June, I worked half a day and came home at noon. Mum was at Queen Alexandra Hospital. The maisonette was quiet, but I could hear running water.

It sounded like the bathroom tap.

The bathroom door was open. Jamie crouched beside the bath, one hand pressed to the metal grille near the heating pipes. His fingers were pushed between the slats as if he were testing the temperature or feeling for a current of air.

"Jamie."

He snatched his hand back and stood. His eyes were red again, as they had been when he returned on Sunday. Not as though he'd been crying. As though he hadn't slept.

"What are you doing?"

"Checking something."

"Checking what?"

"The airflow."

I didn't know what to say, so I nodded and went back to the kitchen.

On Friday, 16 June, I arrived home late, close to nine. Mum was in the sitting room with the television on, but she wasn't watching. She was staring at her mobile.

"Is Jamie home?"

"Yes, but I want to speak to you first."

I sat down.

She said Jamie needed to see someone. A doctor, or at least somebody at an urgent treatment centre. She'd checked the NHS options and found a centre in North End that could assess him over the weekend. If necessary, she would ring NHS 111 first.

"All right," I said.

She'd tried raising it with Jamie earlier. He had shut her down completely and insisted he was fine. When she pressed him, he said he wasn't going.

"Why not?"

"He said hospitals have too many eyes."

I sat with that for a moment.

"Say that again."

"Too many eyes. That's exactly what he said."

I rubbed my face.

"I'll talk to him."

"I don't think talking will work."

"I'll try."

I went to Jamie's door and knocked.

"Come in."

He was at his desk, sitting in the chair and facing the window. The blinds were open. Outside was darkness. He appeared to be looking at nothing.

"Mum's worried about you."

He didn't turn.

"I know."

"She wants you to see a doctor. I don't think that's a bad idea."

"I'm not going."

"Why?"

"Hospitals have too many eyes."

I stood there, trying to understand.

"What does that mean?"

"Too many eyes."

He repeated it in precisely the same tone, as though reading the words from somewhere.

"It doesn't have to be a hospital. It can be a small urgent treatment centre. In and out."

He turned his chair and looked at me. His face was pale, his lips dry and cracked.

"I don't need it."

"Humour me, then. I'll drive you tomorrow after my shift. They'll check that everything's all right, and then we'll come home."

He stared at me for a long time. I couldn't tell what he was thinking.

At last he said, "Okay."

"Okay as in you'll go?"

"Yeah."

"I'll be home by four. We'll leave straight away."

He nodded.

I went back to the sitting room and told Mum he'd agreed to go the following day. She looked relieved.

"What did you say to persuade him?"

"I asked."

"I tried that."

"Perhaps he needed to hear it from me."

She didn't look convinced, but she didn't argue.

That night was quiet. I went to bed at about eleven and didn't hear Jamie moving around the landing. I thought perhaps things were levelling out. Perhaps agreeing to see someone had settled him.

It was a stupid thought, but I had it anyway.

On Saturday, 17 June, I worked a maintenance route around Hilsea industrial estate, replacing panel covers and checking conduit runs. Standard work. I finished a little early and texted Mum to say I was heading home.

She replied asking whether I was still taking Jamie to the urgent treatment centre.

"Yeah," I wrote.

She sent back a thumbs-up.

I reached the maisonette at about quarter to four, parked my work van in the street and went inside. The front door was unlocked.

I immediately felt grit beneath my trainers.

There was a fine layer of grey-white material across the painted floorboards in the entrance. Not much, but enough to notice. It looked like crushed shell grit from a Solent beach.

I followed it into the kitchen. More lay scattered near the sink.

Jamie stood barefoot at the worktop with the tap running. His hands were beneath the water. He rinsed them slowly, turning them over and rubbing his palms together while staring into the drain.

"Jamie."

He didn't look up.

"We're supposed to leave in fifteen minutes."

"Okay."

He didn't move. I stepped closer. The grit on the vinyl was almost white, very fine and mixed with tiny fragments of shell.

"Where did this come from?"

He turned off the tap and dried his hands on his jeans.

"I brought some things back."

"From where?"

"The park."

A trail of shell grit led from the kitchen along the landing. I passed him and followed it. It became thicker near his door.

I pushed the door open.

His room smelt wrong. Salt, wetness and rot. The floorboards near the window were damp and darker than the rest, and clumps of dried brown matter lay scattered across them.

The bedding had been shoved into a heap in the far corner. The desk chair stood against the wardrobe. In the centre of the room lay strands of seaweed, some wet and stringy, others dried and brittle.

Beside them were small broken shells. Some looked like pieces of crab carapace, pale and cracked.

I stood staring.

Jamie appeared behind me. I hadn't heard him walk along the landing. One moment I was alone; the next he was in the doorway.

"What is this?"

"I brought back pieces."

"Pieces of what?"

"Pieces so I wouldn't forget the way out."

I turned to face him. He stood calmly with his hands at his sides and his expression blank.

"What do you mean, the way out?"

"The way back. From the passage."

"You came out on Sunday. Six days ago."

"Yeah, but I need to remember how."

We never reached the urgent treatment centre.

Mum was due to work late at Queen Alexandra Hospital. Before leaving, she had tried to ring the centre and sort out the best time to take Jamie, but by then he had shut himself in his room and refused to answer her. She had to go to work, and I told her I'd keep him in the house and deal with the mess first. The clinic sequence was finished before her late shift began: Jamie had agreed, then refused, and remained inside while I started clearing the room.

At about half past four, Mum texted to say the landlord's managing agent had contacted her. The neighbours downstairs had made a formal complaint about noise and smell. Mum was trying to ring the agent back during her break and smooth things over before it became a threat to our tenancy.

That gave me perhaps three hours before she returned.

I started with the seaweed.

The mound in Jamie's room was larger than it had first appeared. It filled the corner by the window and spread halfway across the floor in a wet, uneven mass. I took black bin bags from beneath the kitchen sink, doubled one inside another and began scooping the weed into them.

It was cold and slimy, coming apart in my hands. Up close, the smell was almost unbearable. The thick stench of salt and decay that had filled the maisonette all week was concentrated there until I could hardly breathe.

I filled one doubled bag, tied it, then started the next. My hands became coated with slime and fragments of kelp. I kept going.

Beneath the weed, the painted boards were soaked. When I pressed my palm against a gap between them, water welled around my skin.

Brilliant. I'd have to deal with that next.

It took three doubled black bin bags to remove all the seaweed. I carried them downstairs one at a time and put them in the communal wheelie bin beside the house. The bags were heavy and leaked slightly, leaving a narrow trail of salt water behind me.

I would clean that afterwards.

Each time I went outside, I expected someone to appear and ask what I was doing. Nobody did. The downstairs neighbours had their blinds closed. I forced the final bag into the wheelie bin and shut the lid.

Back inside, I gathered every towel we had and spread them over the wet boards in Jamie's room. I stood on them, using my weight to draw out the water. They darkened immediately. I wrung them into the bath, returned and repeated the process.

I did it perhaps six times before water stopped rising when I stepped down.

The smell remained. It hung low and heavy, clinging to the plaster. I opened Jamie's window fully. Then I fetched floor cleaner from beneath the kitchen sink and scrubbed the boards with a sponge.

It didn't help much. The moisture had probably worked down between them and into the structure below. At least the surface looked better, less dark and less obviously wrong.

I checked the time. It was 17:40. Mum would probably be home by seven, perhaps earlier if she dealt with the managing agent quickly.

I put the towels in the washing machine, selected a hot wash and added extra detergent. Then I mopped the floorboards along the landing where the seaweed had dripped. The shell grit came up easily but left faint streaks that needed a second pass.

When I finished, I went back to Jamie's room to inspect the floor.

That was when I saw the vent cover.

It lay flat on its back beside the desk. The screws were still caught in it. I looked at the section of wall where it had been and saw the opening.

The original grille had been roughly 20 by 25 centimetres, but the opening was at least twice that size. Its edges weren't clean. Somebody had used a hammer or pry bar to knock away a large section of the lath-and-plaster wall.

The timber laths were broken, their ends projecting at sharp angles. Plaster had crumbled around them.

I stepped closer.

There was no duct behind it. Only darkness. An empty wall cavity leading into the broader service void the landlord had mentioned when we moved in.

I took out my mobile, switched on its torch and shone it inside.

The light reached perhaps half a metre. It showed timber studs running vertically, lengths of old wood about 100 by 50 millimetres, set at roughly 400 millimetre centres. There was no insulation. Beyond the ordinary stud bay, damaged cross-bracing opened into the larger boxed-in void behind the bathroom. It seemed to continue downwards towards the ground-floor crawl space.

The building's original layout made that larger route possible. The deliberate damage made it alarming.

I angled the light upwards.

That was when I saw the scratches.

Four parallel marks ran across one of the studs. They were fresh. The exposed timber beneath was pale and clean against the darkened wood around it.

I shifted the beam and found more marks deeper inside.

The same pattern. Four evenly spaced lines, as though someone had dragged their fingers across the timber while forcing themselves through the service void.

I pulled my hand out and switched off the torch.

The room suddenly felt much smaller.

The smell remained, but now it seemed to come from within the wall rather than the wet floor. I picked up the vent cover and tried to replace it. It wouldn't hold. The screws had been ripped from their holes and the plaster around them was stripped away.

I leant the cover against the opening instead, left the room and closed the door.

Mum came home at quarter past seven. I was at the kitchen table with a bottle of lager I hadn't opened. She put her bag on the worktop and rubbed her face with both hands. She looked exhausted.

"Did you speak to them?" I asked.

"Yes."

She poured herself a glass of water.

"I smoothed it over. For now."

"What did you tell them?"

"That we'd deal with it. That it wouldn't happen again."

She drank half the glass in one swallow and set it down.

"Is Jamie home?"

"He's in his room."

She nodded but didn't move. I opened the lager and took a drink, then put the bottle down.

"He's been inside the walls."

Mum turned towards me. Her face went pale for a second. Then the colour returned and she frowned.

"What are you talking about?"

"The vent in his room. He pulled it off and smashed out the wall behind it. The cavity connects to that larger service void and the crawl space beneath the house. There are fresh scratch marks on the timber. He's been climbing through it."

Mum stared at me without speaking.

"I'm serious. Go and look."

She put down her glass hard enough to spill water.

"Stop."

"Stop what?"

"This."

She gestured towards me. Her hand shook.

"He's grieving, Callum. He's trying to process what happened. He doesn't need you accusing him."

"I'm not accusing him of anything. I'm telling you what I saw."

"He lost his father four months ago. You know how hard that's been for him. For all of us."

Her voice rose.

"He needs support now, not this."

I didn't answer.

She folded her arms.

"Did you talk to him? Did you ask him about it?"

"No."

"Then how do you know it was him?"

"Who else could it be?"

Mum did not answer. She looked towards the hall, then back at me.

"I'll talk to him," she said. "But you need to stop doing this. Stop looking for problems."

I drank the rest of my lager and set the bottle down. Mum walked past me into the hall.

I heard her knock on Jamie's door, heard it open, then her voice, low and careful. Jamie answered, but I could not make out the words. I got up and went to the hallway.

Mum stood in Jamie's doorway with her arms still crossed. Jamie was sitting on his bed in the same position as before, fully dressed, trainers on. He was looking at Mum, but not quite at her face. His eyes tracked her mouth.

"Your brother says you've been inside the walls," Mum said.

Her voice was softer now, carefully calm. Jamie did not respond at once.

Mum waited.

Then he said, "No."

His voice sounded wrong. Not different, exactly, but delayed. There was a gap between his mouth opening and the sound coming out. Beneath it, barely audible, I heard something else.

Another sound trying to match him. Trying to synchronise.

Mum's shoulders relaxed slightly. "All right. That's what I thought."

Jamie kept watching her mouth.

"He's just worried about you," she said. "We both are."

"I know," Jamie said.

The same delay. The same doubled sound underneath.

Mum smiled, but it did not reach her eyes. "Get some rest, all right?"

Jamie nodded. She closed his door and returned to the kitchen. I followed.

She picked up her glass and finished the water, then turned to me. "He said no. I heard him. So perhaps you were wrong."

I said nothing.

She sighed. "I'm going to bed. I can't do this tonight."

She left. I stood in the kitchen for another minute, then took my keys from the worktop and walked out.

I drove to the seafront car park beside Bransbury Park because I did not know where else to go. It was nearly eight and the car park was mostly empty. I parked near the far end and sat with the engine off and the windows cracked.

The unease did not leave. It followed me out of the maisonette, into the van and all the way there. It sat low and heavy in my chest, the same way the smell had settled throughout the house.

I kept seeing the scratches in the wood. Kept hearing Jamie's delayed voice and that other sound beneath it, trying to match.

I stayed until it was dark. Then I drove back.

I reached Eastney at about half past nine. The maisonette was dark except for the kitchen light. I parked on the street, locked the van and went inside.

Mum lay on the sofa, still dressed and wearing her shoes, curled on her side with one arm tucked beneath her head and the other hanging over the edge. Her eyes were closed. Her breathing was even.

I shut the door quietly. She did not move. I went over and said her name.

Nothing.

I said it again, louder.

She stirred, opened her eyes halfway and blinked at me as if she did not know where she was.

"Hey," I said. "Are you all right?"

She sat up slowly and rubbed her face.

"What time is it?"

"Half past nine."

She looked around the room. Her handbag was on the coffee table. The television was off. She frowned.

"I don't remember lying down."

"You were out cold."

She shook her head. "I was just sitting here. I was going to fold the washing."

I glanced at the basket by the television. It was full and untouched.

"When did you get home?" I asked.

"About six."

She rubbed her eyes. "I sat down for a minute. That's all I remember."

I said nothing. She looked at me, then past me towards the hall.

"Is Jamie home?"

"I've only just got back. I'll check."

I walked down the hall. His door was closed.

I knocked. No answer. I opened it.

The room was empty.

It still smelt of salt and rot, though more faintly now. The window remained open. The floorboards were damp, but not soaked. The vent cover was back on the wall.

I stopped. It had been off when I left.

I crossed the room and crouched beside it. The cover had been fastened in place, but sat at an angle. One corner was higher than the other. The screws were in, though not fully, as if someone had forced them into stripped holes that could no longer grip.

I took out my mobile and checked the time. 21:32. I had not been home since 17:40. Nearly four hours.

I stood and returned to the sitting room. Mum was still on the sofa, pulling her hair back into a ponytail.

"He's not here," I said.

She looked at me. "Did he leave a note?"

"No."

"Have you texted him?"

I took out my mobile and sent a message.

Where are you?

It did not deliver. I showed her the screen. She sighed and leant against the cushions.

"He probably went for a walk," she said.

"At night?"

"He's done it before."

I did not argue. I went to the back door and checked the lock. It was unlocked. I opened it and stepped onto the small concrete landing. The security light clicked on.

The back garden was narrow, mostly bare earth, with a couple of shrubs beside the fence. The gate was closed. I looked down at the aluminium channel beneath the door.

Shell grit had been ground into it. Fine, grey-white particles, the same as the stuff I had cleaned up earlier.

I crouched and touched it. It was gritty and cold.

I went inside and locked the door behind me. Mum was standing in the kitchen, pouring herself a glass of water.

"Anything?"

"The back door was unlocked."

She paused midway through pouring. "Did you lock it this morning?"

"I don't know. Probably."

She set the glass down. "He must have gone out that way."

"Yeah."

She looked at me. "You don't sound certain."

I did not answer.

I returned to Jamie's room and pulled the vent cover from the wall. It came away easily. The screws had barely held.

I set it on the floor and shone my mobile's torch through the opening. Beyond the broken lath and plaster was the enlarged wall cavity, opening into the broader service void we had been told ran between parts of the converted house. The timber studs began less than a metre in, spaced at roughly 400 mm centres. The scratches were still there.

Now there was something else.

A soft, steady hum. Almost a vibration. Not mechanical. Not electrical. Just a hum.

I leant closer.

The sound shifted. It moved rather than staying in one place, travelling along the studs from left to right, then back again.

I pulled away. The hum stopped.

I waited. Ten seconds. Twenty.

It began again, fainter now and farther away, moving downwards towards the broader void beneath the floor and the ground-floor crawl space.

I replaced the vent cover and left the room.

I sat on my bed and rang Dan Mercer. He answered on the third ring.

"Yeah?"

"I've got a question."

"Go on."

"What should an old service void look like in a divided Victorian house? The place has cast-iron radiators, but there's a vent in one bedroom."

He was quiet for a moment.

"Are you talking about heating ducts or something else?"

"A wall vent."

"Those houses weren't built with warm-air systems. They'd have used fireplaces originally, then radiators. If there's ducting, someone added it later."

"So the ordinary wall cavities wouldn't be built for airflow?"

"No. Standard timber studs behind lath and plaster, probably at about 400 mm centres. Old wiring or conduit, maybe insulation if you're lucky. Why?"

"There's a vent in my brother's room. The cover came off. The opening behind it is much bigger than it ought to be."

"How much bigger?"

"At least twice the size. And it goes back into a larger void."

Dan did not answer immediately. I heard him shift, perhaps sitting up.

"That isn't normal."

"I know."

"Someone's altered it. Knocked out the laths, pulled away whatever was behind them. Any damage to the framing?"

"The edges are rough. Splintered."

"That's a problem."

"Why?"

"Because nothing inside a normal wall should be large enough for a person. If someone's opened it into a service void, you could have mould, asbestos in old materials, structural damage if they've cut a stud, or worse."

"Worse how?"

"Squatters. Drug users. Someone using the void to move between parts of the building or get from the crawl space to the upper floors. I've seen it twice. Once in a pre-war conversion in Portsmouth, once in an old terrace in Landport. People cut through walls so they can move about without being seen."

I did not speak.

Dan continued. "You need to have it inspected. Managing agent, landlord, whoever deals with the building. And don't go poking around in there. If someone's been inside those walls, you don't know what they've left behind."

"All right."

"I'm serious, Callum. Ring someone."

"I will. Tomorrow."

"Good."

He ended the call.

I sat there holding the mobile. Squatters. That made sense. That was something I could deal with.

Someone breaking in and using the voids to move around, perhaps stealing things or hiding there. That could be fixed.

I did not let myself think about the scratches or the hum.

Morning came too quickly.

On Sunday, 18 June, I got up at about six, showered and went to the kitchen. Mum was already awake, sitting at the table with both hands around a mug of tea. She looked as though she had not slept.

"Did Jamie come back?" I asked.

She shook her head.

I checked my mobile. No messages. I called him. It went straight to voicemail.

"We need to call someone," I said.

Mum looked up. "Who?"

"The police. Report him missing and vulnerable."

Her face tightened. "He's fine. He's just out."

"He's been gone all night."

"He's done that before."

"Not like this."

She set down her mug. "I'm not calling the police on my son."

"It isn't calling them on him. It's asking them to find him."

"He doesn't want to be found right now. He needs space."

I pulled out a chair and sat opposite her. "Mum, something is wrong."

"I know that."

"Then let's get help."

She looked at me. Her eyes were red.

"They'll think he's on drugs or having some sort of breakdown. They'll take him away."

"Perhaps he needs that."

Her jaw tightened. "No."

I did not press her. Not yet.

She stood, crossed to the sink and poured away the rest of her tea. Then she turned and stared past me towards the hallway.

She said nothing. She just stared.

I turned. There was nothing there.

"What is it?"

She walked past me into the hall. I followed. She stopped outside her bedroom, looked down at the floor, then into the room.

I came up behind her. "What?"

She pointed to her bed. To the pillow.

The white pillowcase had been clean. Now fine grey-white shell grit lay across it in a narrow line, as if someone had stood over her while she slept and let it sift from their hand.

She did not move or touch it. She only stared.

"Call them," she said.

The officers arrived at 08:43. A woman and a man. The woman introduced herself as PC Asha Webb. The man was PC Tom Reed. Both were from Hampshire and Isle of Wight Constabulary, and both looked as though they would rather have been somewhere else.

Mum let them in. I stayed in the kitchen.

PC Webb did most of the talking. She asked when we had last seen Jamie, whether he had been behaving unusually and whether there had been any arguments or threats.

Mum answered carefully. She told them about Dad's death, Jamie's ferry trips, Fort Victoria and the seaweed.

She did not mention the walls.

PC Webb wrote everything in a small notebook. PC Reed stood near the door with his arms folded, scanning the room.

"Any history of mental-health problems?" he asked.

Mum hesitated. "No."

"Drug or alcohol misuse?"

"No."

"Any medication?"

"No."

PC Reed nodded but did not look convinced.

PC Webb turned a page in her notebook. "Has he threatened to harm himself or anyone else?"

"No," Mum said. "Nothing like that."

"And you're certain there wasn't an argument? A disagreement about something?"

"No. He's just been quiet."

PC Webb looked at me. "You live here as well?"

"Yes."

"When did you last see him?"

"Yesterday, at about five."

"How did he seem?"

"The same as usual."

"Which is?"

"Quiet. Keeps to himself."

PC Reed shifted his weight. "And you didn't think that was worth mentioning before?"

I looked at him. "Mentioning what?"

"That he's been behaving differently."

"I didn't say that."

"You said he's quiet and keeps to himself. After losing his father, that could be significant."

I did not answer. PC Webb intervened.

"We're only trying to get a complete picture. Is there anything else we should know?"

I glanced at Mum. She was staring at the floor.

"Yes," I said. "There's something in the walls."

PC Reed frowned. "What?"

"In his room. There's a vent. Someone took the cover off and broke through into the wall cavity. The opening connects to a service void big enough to crawl through."

PC Webb's expression did not change. "Show us."

I led them along the hallway. Mum followed. I opened Jamie's door and stepped aside.

The smell reached them first.

PC Webb wrinkled her nose. PC Reed pulled a face.

"What is that?" PC Webb asked.

"Seaweed," I said. "He brought it back from the island. I cleared most of it out yesterday."

I crossed to the vent and removed the cover. It came away easily.

Both officers stepped closer. PC Webb shone her torch into the opening. PC Reed leant beside her.

"It's an old building," PC Webb said. "Lath and plaster, later alterations. It may have been like this for years."

"No," I said. "The edges are fresh. Someone broke through."

PC Reed looked at me. "Did you see anyone do it?"

"No."

"Then how do you know?"

"Because the plaster is freshly broken, the wood is splintered and there are scratches inside. I work around old buildings and service spaces. I know what age and damp do to timber. That damage is new."

PC Webb angled the torch.

"I don't see any scratches."

"They're farther in, on the studs."

She moved the light, paused, then drew back.

"Could be rats," she said.

"They aren't rat marks."

PC Reed folded his arms. "You think your brother did this?"

I did not answer.

"Has he shown signs of self-harm? Paranoia? Hallucinations?"

"No."

"But he's been behaving strangely."

"Yes."

"And now he's missing."

"That's why we called you."

PC Webb put away her torch. "We'll file a missing-person report and circulate him as a missing and vulnerable adult. If officers find him, they'll check that he's safe."

"That's it?" Mum asked.

PC Webb looked at her. "That's what we can do at present. He's an adult. There's no clear evidence of foul play or immediate danger."

"What about the shell grit?" I asked.

"What shell grit?"

"On her pillow. Someone put it there."

PC Reed looked at Mum. "Did you see anyone in your bedroom?"

"No. I was asleep."

"Were the doors locked?"

"I thought so."

"Windows?"

"Closed."

PC Reed nodded. "It may have been carried in on clothing or footwear. Easy enough to miss."

I stared at him. "You think she scattered it over her own pillow?"

"I think there are several explanations that don't involve somebody breaking in."

The front door opened.

We all turned.

Jamie walked in.

He was smiling too broadly, showing all his teeth, his eyes bright.

"Hello," he said. "Sorry. Just went for a walk."

Mum exhaled and moved towards him. "Where have you been?"

"Around."

"All night?"

"Lost track of time."

PC Webb stepped into the hall. "Are you Jamie Price?"

He looked at her. His smile did not change. "Yes."

"Your family have been worried about you. Are you all right?"

"I'm fine."

"Where have you been?"

"Walking."

"All night?"

"Yes."

PC Reed came closer. "Have you taken anything? Medication or drugs?"

Jamie's smile widened. "No."

"Are you sure?"

"Yes."

I looked at his cuffs. They were wet, dark with water, and carried the same smell of salt and rot.

Behind him, a thin grey smear crossed the wall at roughly shoulder height, as if something soaked had brushed against it on the way inside.

PC Webb followed my gaze. She looked at the smear, then back at Jamie. She said nothing.

PC Reed took out a card and handed it to Mum. "Ring us if anything changes."

Because Jamie was alive, apparently competent and denying that he needed help, the officers cancelled the active missing-person circulation before they left.

Mum stood in the hallway, staring at him.

Jamie kept smiling.

I looked again at the grey smear. Neither officer mentioned it.

That night the maisonette became quiet.

Not ordinary quiet. The kind that felt wrong.

I lay in bed staring at the ceiling, my mobile on the bedside table. Mum's bedroom door had closed at about eleven, and the sound still sat in my head. The officers had gone that morning after taking notes, asking more questions and confirming that Jamie was alive. Mum had watched them leave and returned looking smaller than usual. She had gone straight to her room without speaking.

I kept waiting for Jamie's door to open. For footsteps in the hall. For anything.

Nothing came.

The silence pressed down harder the longer I lay there. No radiators ticking. No traffic from the street. No wind against the windows. Only a silence that seemed to be waiting for me to fall asleep.

I rolled onto my side and checked my mobile. 00:30.

No messages. No missed calls.

Then the cast-iron radiator clicked.

I had heard that before. Old radiators sometimes ticked when the heating came on and the metal expanded. Normal.

This did not stop.

Tap. Pause. Tap. Pause. Tap.

Then four taps, a pause, two taps, a pause, four taps.

Slow. Steady. Deliberate.

I sat up and stared at the radiator beneath the window. The room was cool. The heating was off.

Four taps. Two. Four.

I got out of bed and crouched beside it. I held my hand near the metal.

Cold. No warmth at all.

Tap.

I pressed my ear to the pipe.

The sound was not coming from the radiator. It was coming from inside the wall.

Beneath it, faint but unmistakable, was the hum.

The same hum I had heard through the vent in Jamie's room. Low and steady and not mechanical. It moved along the studs, shifting from left to right as if something were following the framing.

I drew back.

Then the smell reached me. Salt and rot and low tide, thick enough to taste.

I stood and backed towards the door. The hum continued, closer now, directly behind the radiator pipe.

Right there.

I grabbed my mobile and opened the bedroom door.

Jamie stood at the far end of the hall near the bathroom, his forehead pressed against the wall.

He did not move. He simply stood with his arms at his sides, bare feet on the painted boards and his head tilted forwards so his face lay flat against the paint.

Then he rocked.

Only slightly. Forwards and back. As if testing the wall, feeling for a seam or weak point.

I said his name.

He did not respond.

I said it again, louder.

He rocked once more. His shoulders shifted. His head pressed harder against the wall.

I reached for the hall switch and turned on the light.

"Stop," I said.

Jamie stopped rocking.

Then he turned.

His eyes were cloudy. Not red any longer. Clouded at the edges, with pupils far too wide. His lips were split down the middle and wet. Not bleeding. Just wet.

Salt water ran from his chin in a thin line and struck the floor without a sound.

His shoulders moved wrongly, out of time with his hips, as though something inside him were adjusting, settling and trying to get his proportions right.

I stepped back.

Jamie stepped forwards.

I turned, ran into the bathroom, slammed the door and locked it. I switched on the light and pulled out my mobile with shaking hands.

I dialled 999.

It rang twice.

"Emergency. Which service?"

"Police and ambulance," I said. "My brother... something's wrong with him."

The call was transferred. A woman's voice came on, calm and professional.

"Police control room. My name is Claire. Tell me what's happening now."

"He's in the hall. He doesn't... He doesn't look right."

"Is he injured?"

"I don't know. Maybe. His eyes are wrong. He's..."

Something moved outside the door. Heavy. Dragging.

I stopped talking.

"Sir, are you still there?"

"Yes."

"What's your address?"

I gave it to her. My voice did not sound like mine.

"Is your brother threatening you?"

"I don't know."

"Are you safe where you are?"

"I'm in the bathroom. The door's locked."

"Good. Stay there and keep the door locked. I'm sending officers now, and ambulance assistance is being arranged. I'm going to stay on the line until they arrive. Can you do that?"

"Yes."

The dragging sound moved past the door. Slow and deliberate, like something heavy being pulled across the floor.

Then it stopped.

I stared at the door and held my breath.

The extractor grille above the bath rattled.

I looked up. The metal grille, roughly 20 by 25 cm, shook once.

Stopped.

Shook again.

Dust fell through it, fine and pale, settling on the porcelain.

Then came shell grit.

Wet grey-white grit trickled through the slats and pattered softly into the bath.

"Sir, are you still with me?" Claire asked.

"The vent," I said.

"What about it?"

"Something's inside it."

The grille bowed. The screws holding it groaned.

"Officers are about three minutes away," Claire said. "Stay on the line."

The grille tore free and fell into the bath with a clang.

A hand pushed through the opening.

Pale. Waterlogged. Fingers too long, their joints bending the wrong way.

I backed against the basin.

The hand reached down and felt along the tiles, dragging wet shell grit behind it.

Then Jamie spoke outside the door. His voice was calm and quiet.

"You don't need to be afraid."

I did not answer.

"You just need to stop locking things."

The hum began again beneath his voice, agreeing with him.

I heard sirens, faint but approaching.

Jamie continued. "It's easier if you don't fight."

The bathroom door shook under a violent impact.

Someone, or something, had thrown its full weight against it.

I yelled. I could not help it.

Claire's voice was in my ear. "Callum, officers are arriving now. Stay where you are."

The door shook again. The frame cracked.

"It's coming through the vent!" I shouted.

Heavy boots sounded in the hall. Voices called out commands.

I looked up at the opening.

A face filled it.

Jamie's face, compressed into a gap too small to admit his head. Cloudy eyes. Open mouth. Water dripping from his chin.

Then it withdrew too quickly, as though something had yanked it away.

There was a crash in the hall. Bodies struck the wall. Voices overlapped.

"On the floor! Now!"

A struggle. Furniture scraping. Something breaking.

A Taser cracked once, then again.

One of the officers shouted that Jamie had a weapon. Another shouted for armed support. Claire told me to stay down. There was more crashing, a scream that did not sound human, and a voice outside yelling that he was attacking the officers.

The authorised firearms officers arrived within moments, already nearby and diverted when the first constables reported the immediate threat.

There was a final impact against the bathroom door. A roar. A firearms officer shouted a warning.

Then came three gunshots, close together and loud enough to leave my ears ringing.

The hum stopped in the middle of a note.

Silence.

I stood against the basin, breathing too quickly, the mobile still pressed to my ear.

"Callum?" Claire said. "Officers have secured the scene. Someone will come to you. Stay where you are and try to keep calm."

Footsteps approached the door.

A knock.

"It's PC Webb. You're safe. I need you to unlock the door."

I did not move.

"Callum, it's over. Unlock the door."

Something slid beneath it. PC Webb's warrant card.

I bent and picked it up. My hands were still shaking.

I unlocked the door and opened it.

PC Webb stood in the hall. There was wet shell grit on the shoulder of her uniform. Her face was controlled and professional.

Behind her, Jamie lay beneath a white sheet already darkening with stains. Wet grey-white grit surrounded his head in a broad circle.

I handed back her warrant card. She took it.

"Are you hurt?"

I shook my head. I could not speak yet.

PC Reed stood farther down the hall near Jamie's room, speaking into his radio. Two firearms officers were by the front door. Paramedics waited behind them with their equipment.

PC Webb looked at me.

"The initial assessment is that your brother was experiencing an acute mental-health crisis. The control room recorded threats, and the first officers reported an immediate attack. A Taser was ineffective. When the armed officers arrived, he launched himself at them and they believed there was an immediate threat to life. They fired to stop him."

I stared at the sheet.

"Had he taken anything?" PC Webb asked. "Any drugs you know about?"

"No."

"Are you certain?"

"Yes."

She wrote in her notebook.

"Nothing obvious was found on him. No tablets, needles or drug paraphernalia."

PC Reed came over.

"There's more shell grit inside the service void," he said. "Seaweed as well. A whole wet trail runs through the vent, down into the ground-floor crawl space. Smells like the Solent under there."

PC Webb looked at him. "Any other access points?"

"The damaged opening in the bedroom and the external crawl-space hatch. Nothing else we've found."

"A second person?"

"No."

PC Webb turned back to me. "Had your brother been going into the water? Swimming or diving?"

"I don't know."

"Did he bring anyone here? Friends or strangers?"

"No."

She nodded and wrote more notes.

Mum came out of her bedroom in her dressing gown. Her face was pale and blank. She looked at the sheet, then at me, then at PC Webb.

"Mrs Price," PC Webb said, "I'm very sorry."

Mum did not answer.

Two days later, I moved Mum into Ruth Ellis's spare room in Cosham. Ruth worked with her at Queen Alexandra Hospital. She did not ask many questions.

Mum packed one suitcase. I loaded it into my work van. She did not look back at the maisonette when we left.

A week later, I returned with Dan to isolate the consumer unit and collect anything we had left behind. Dan did not ask why I wanted him with me. He simply came.

We worked quickly. I switched off and checked the circuits while Dan gathered tools and boxes from the kitchen. We barely spoke.

I was in the hallway near my old room when the cast-iron radiator clicked.

Once.

I froze.

Dan stopped in the kitchen doorway and looked at me.

We both waited.

The silence held.

Nothing else came.

"Let's go," Dan said.

I nodded.

We left, and I never went back.

I kept one thing. Jamie's mobile. The police returned it with his other belongings after they had finished examining it.

I switched it on once and went through his photographs until I found the one taken at 02:53 on Saturday, 10 June. The image had been geotagged near Hurst Point, across the Solent near the western end of the Isle of Wight, though Jamie had supposedly been exploring the abandoned fortifications beneath Fort Victoria.

It was the last photograph he sent Mum before everything began.

I enlarged the dark mouth of the fictional sealed passage beneath the fort. In one corner was the grey blur I had assumed was the edge of Jamie's rucksack strap slipping into the frame.

I zoomed in.

It was not a strap.

It was a shoulder leaning into the photograph beside Jamie, close enough to touch him. Real enough to be there. Blurred enough to deny.

I enlarged it again.

And again.

The pixels broke apart. The image dissolved into noise.

But I kept looking.