London, potbound, winds its roots deeper into the clay soil of its basin and pushes upwards, questing for sunlight above its flyblown glass canopy. Fox Tower was one of three (Winslow and Pastor were its siblings), as rooted in the ground as it was possible to be with 22 floors sprouting from its grim, piss-soaked core. The stench of everything clung to it, a feast of human waste fertilising its foundations as, inside, people lived through a thousand lives every minute.

It was not the sort of place Michael would choose to live in. His life had been lived in nicer parts of London, save for his time at university in Staffordshire. He would not even visit somewhere like Fox Tower, given the option, but the option was not there. Pettigrew, his dog, had slipped the leash and made a run for the front entrance, flying past the barely there front door into the slate grey darkness inside.

Fox House reared into the flat sky above him, encircled by a sparse vortex of dry, joyless snowflakes. Every floor was wrapped in balconies, and every balcony was a riot of bric-a-brac; broken bicycles, hard plastic rocking horses, laundry airers, half-inflated plastic footballs. They were not used to admire the view, even if there was anything worth seeing. Michael wondered if Pettigrew was even now sniffing at the doors to those flats, and how far up she might have got. ‘Petty?’ he called, tentatively. ‘Petty! Here girl, back here!’ It was pointless – he was going to have to go in.

He marched across the forecourt of the estate – at one time it would have had grass, but now it was little more than a tarmac strip bisecting a stamped-hard field of dust. The snow fell on it and disappeared, unable even to turn it into mud. An optimistic cherry tree, blasted into brittle submission, stood guardian. A young man slouched past, barely slowing as his path crossed Michael’s. Michael was forced to do a ridiculous little dance to avoid crashing into the man, who didn’t turn his hooded head. Michael, who didn’t even dare mutter under his breath, carried on to the tower. The door was unlocked, and swung outwards without a whisper. Why outwards? Harder to kick a door in if it opens outwards, he thought. Inside was a gloomy concrete reception hall. Glancing up at the decrepit security camera trained on the door, hoping it was working and that it would record his face, Michael stepped inside.

The silence inside was smothering, folding itself gently around Michael the instant the door tapped closed. It slipped cosily down his spine and caused him to shudder. It’s just a block of flats, he told himself. And all you want is your dog.

Where was Pettigrew? He’d expected to find her investigating some exciting smells in the hallway – certainly there were enough in here to keep a dog happy for a while. Instead he found an empty, concrete room more like the stairwell of a multi-storey car park than a reception. There was a metal desk bolted to the floor that may once have been the post of a concierge, back on the drawing board of a blissfully ignorant architect, surely never in real life. Two lifts sat dimpled and dull beneath a fluorescent lampshade as full of insects as it was of light. One set of doors sat partially open, a mouth gaping for food. He was glad that they were out of the question for him – he needed to go up the stairs or risk missing Petty between floors.

The stairwell was no more inviting, but at least there were windows. He called up, hoping to hear the soft clatter of claws in response. Nothing, again. He craned to see how far the stairs went – high, dizzyingly high, he snapped his head back down before he fainted. This was a street built horizontally, longer than the short suburban terrace he lived on and straight up into the sky. How people lived at the top he couldn’t imagine. A family life built in the air; no roots, no foundation, everything balanced at the top of a pile of other lives. Roots there would tangle with the lives of the people below, everyone interdependent in their boxes in the sky. Do the people at the bottom of the tower feel it bearing down on them?

Something moved, to his right, by the doors. From the corner of his eye, it looked big enough to be Pettigrew. He was about to call to her when he saw what it actually was – rats. A cluster of them, maybe ten or fifteen, squeaking and slipping as they moved towards the stone steps. He squirmed in revulsion at the sight of the glistening, ragged fur-covered bodies scrambling over each other in a mass of stinking life. With the rats between him and the doors, he ran up the stairs, clearing two at a time in a stumbling panic.

The door to the first floor balcony slammed emphatically behind him, leaving him in a stark corridor lined with blue doors. The paint was chipped and peeling on some, bright and fresh on others. One showed signs of having been recently bashed in – police or criminal activity? Twisted faces leered from the cheap, knotted plywood that plastered over its scars.

The flourescent hum of the lights did little more than add an accent to the silence on this floor. She could be round the corner. Michael shook his head, reassuring himself that this wasn’t, in truth, a very scary place. Nothing worse than walking down a street in an unfamiliar neighbourhood. A street with no sky, no exits other than the one he came in, with nothing but rows of doors, no witnesses… the CCTV camera buzzed lazily round to stare impassively into his face, and he corrected his train of thought. Someone will see me. Someone knows I’m here. He walked as boldly as he could manage.

From behind him, chattering voices crowded into the corridor as a door opened. Though it was early in the day, Fox Tower was starting to wake up. The door slammed shut, and the voices disappeared behind it. Michael did not turn around, not wishing to make eye contact or even acknowledge his presence here.

“Excuse me. What are you doing here?” He stopped and turned around. The woman behind him wore a neatly ironed grey uniform and ragged, greying trainers. Her hair, you’d call it red but it was orange – the colour of a blonde under a sodium lamp. His throat, dry and unprepared for speaking, struggled to supply his mouth with a voice to answer.

“My dog,” he swallowed as he said it, gulping the last letters down. “My dog, Pettigrew. Petty. My dog came in here. She ran away. From me, she ran away from me. Have you seen a dog?” At the last sentence, his middle-class certainty of purpose reasserted itself and he sounded, in his head, almost normal.

“This is a safe place,” she hissed, putting unusual emphasis on the phrase ‘safe place’. “You’re not supposed to be here. We are protected.”

“I’m… I’m really just here for my dog!” what did she think, that he was here on the rob? That he was a drug dealer, in his Selfridge overcoat and scuffed Converse (a white guy in a Selfridge overcoat and scuffed Converse, his mind muttered, guiltily)?

“You don’t understand,” she said, urgently. “We are protected. You shouldn’t be here. And certainly not today. Your dog… Your dog will be fine. Go.” When he didn’t move, her mouth twisted with contained annoyance and she brushed past him to the lifts. As she waited for her lift to arrive she turned and called to him. “And don’t use the stairs!”

Petty was not on this floor. he found that, round the corner, there was nothing but another door leading onto the stairwell at the other end of the block. It was as empty as the other, but not as well-lit. There were no windows here, just a gap in the walls, a slash through the concrete blocks bandaged with gauzy chicken wire. Here and there, holes were large enough to fit a person through. We are protected, he thought to himself. Really? Not very well.

A snowflake blew in through the chicken wire and landed on his arm. It did not melt. Why is it so cold in here? This whole block is freezing, but the woman he met earlier had her coat over her arm so the flats, at least, must be warm. At this time of day he pictured them as frowzy human dens – windows closed to keep the heat in, thin curtains drawn against the grey soup of the weak morning light. Families crowded into three rooms like our ancestors in straw-walled roundhouses. The ancient intimacy of close quarters.

Bleary Balearic beats slouched down the stairwell, a promise of a summer that was showing no signs of coming, or memories of one spent elsewhere. It would be waking, now, those in the flats all round. Soon this block would empty as its inhabitants, but not its denizens, trooped off to work. He needed to find Pettigrew, soon. The thought that she may have gone back outside struck him and he pressed his forehead against the chicken wire to see if he could see the front yard of the building.

Nothing. Really nothing; he was only two floors up and the ground had vanished into a thick fog. He could see it lying across the area for miles, a haze as it reached the skyline of the City to the west. Fox Tower was an island, now, a drowned spire jutting from a sea of nothing.

“PETTY!” he shouted, using his full volume for the first time, his voice echoing madly around the flat spiral of the stairs. From somewhere there came an answer, a single bark. Well, she was still in the building, then.

He found no sign of her on the second or third floor. He was wondering if he was just being an idiot when he got to the fourth floor. Maybe she’d gone back down the stairs. He’d been using the second stairwell, traipsing back to it whenever he finished a sweep of the floor, because he didn’t like the idea of going back to the rat-infested one, but he’d have to check just in case.

Something was wrong with this stairwell. It was dark, much darker than it had been earlier, and darker even than the windowless one. The fog had crawled up the side of the building and the sun had disappeared behind a deep-black cloud filled with the last trick of Winter. Staring at the sky, he caught the reflection of a door opening on the floor above. Someone looked out, then vanished back in.

“Petty?” Michael’s call was quieter this time, but the echoes were stronger, stranger, louder than his voice had been. The door behind him bumped closed, a series of gentle wooden knocks. It almost sounded as if it wanted his attention. He glanced back at it – at eye height, scratched into the safety glass of the small windows, were the words WE ARE PROTECTED. “Petty!”

Again the bark came back to him, closer than before, echoing down from the floors above. he climbed to the fourth floor, wondering if the person he had seen look out the doors would still be there, if they’d seen his dog. He got the feeling they wouldn’t say if they had. He wasn’t supposed to be here. On these doors were painted in Tipp-ex WE ARE PROTECTED. He hadn’t noticed it on the other doors of the building. He hadn’t been looking.

The door opened onto the same kind of corridor as all the other floors, indentical but for the light. None of the fluorescent tubes were on, the only light coming from the emergency exit signs and a sickly yellow glow from the lifts. Michael did not want to walk down this corridor. He knew that someone had been hanging around on this floor and the light being out was a bad look for a bad place. On the other hand, he had heard Petty barking and was fairly sure it was this floor.

“Petty?” he stage-whispered. There was an answering whine from somewhere in the darkness. “Here, girl, come on!” There was no movement, so he had no choice but to pad as silently as he could along the corridor. “’sake, Petty, just come here so we can go.” The whining came again, closer. The lifts.

The same wan light hung above the two sets of doors as he’d seen in the lobby, a rectangular block that served as a mass graveyard for curious insects. It illuminated almost nothing, and again there was one set of doors partially open. Inside it was dark, but Pettigrew’s keening whine came from within. Pushing himself as hard as he could, Michael slipped sideways between the malfunctioned doors.

It was black in the lift, a smothering darkness that made the light in the corridor outside look like day. Michael knew immediately that Petty was not in here with him, though perhaps something else was. Before he could leave, the doors slid closed, neatly and with a silence that did not fit with their dented, worn condition. He couldn’t move; the shock of what was happening had frozen his limbs.

A light came on. Gentle, red, an arrow pointing down. The lift jerked and descended, taking him to the ground floor. To the lobby. To the front door. He could just go, get out of this hateful ugly block with its broken lights, its weird inhabitants, its hungry lifts, Petty would come out if he just waited for her. Angry, he found himself able to move again, jabbing at the down arrow as if he could accelerate the journey with the sheer force of his desperation.

The doors opened, but it was not to the lobby. The lift had overshot and he was now in the car park. It was exactly as depressing as he would have expected it to be, had he thought it was going to exist. He didn’t want to stay in the lift a second longer, and the stairwell was immediately obvious, looking out, to his left.

More music echoed through the car park. Different this time. Dolorous singing over hard, industrial rhythms. Barely music at all, more like someone hitting an iron bar on a shopping trolley. Unsettled, desperate to leave, Michael sped up to reach the stairwell. The clattering, clashing music raised its metal voice to follow him out.

When he opened the door, he realised his mistake. Three figures stood in the lowest part of the stairwell – which, he realised, did not go anywhere. He thought, too late, about the stairs he had been in earlier. They only went up, there was no way down to this area. The figures wore grey hoodies, and they faced away from the door. Candles – cheap, off-white pillars that would usually be kept in storage for a power-cut – were dotted around and provided the light. Graffiti covered the walls, but there was no variety. No tags, no pictures. Just the phrase WE ARE PROTECTED.

The nearest figure turned to him. It wore a mask, the face stern to the point of anger with a painfully knitted brow and a golden beard. It was familiar, somehow, like an image from a parade. The voice that came through it was that of a young man.

“The fuck you doin’ here, man?” he said, and without ceremony stabbed Michael in the stomach before turning back to his companions. “Later every year, swear down.”

There was a drain, or something, set in the floor. He stared at the feet of the people who had attacked him as his blood flowed into the grate. A pair of red Converse. Ragged, greying trainers. Polished brogues. Nice social mix in here, he thought as he passed out.

Michael woke to Petty licking his face. He put his hand up to stroke her, but it fell back weakly. The grass he was lying on felt springy and comforting on his cheek. A fat black spider crawled determinedly past his sightline, away from Pettigrew. He was outside, he realised, lying on some grass with his dog. Not dying in a windowless stairwell. His stomach didn’t even hurt.

He sat up. He was on the lawn outside Fox Tower. The weather had turned, and he felt better for the sun. Petty ran backwards, then in a small circle, the random pattern generation of an excited dog. What had happened? Was all that just a mad fantasy as he lay on the grass out here? He checked his clothes.

His shirt had a ragged hole just below his sternum, his trousers saturated with blood blackened and clotted in the air. He vomited, but his stomach was simply in spasm, drawing up nothing. Petty shied away, confused.

What was wrong with her? He straightened up. His blood pulsed in his feet, making them throb in his shoes, which he took off, curling his toes into the grass. The taproot of the building came questing through the soil to meet the urgency of his blood. There’s nothing to worry about. This is a safe place, he thought as the daisies bloomed around him in the afternoon sunshine. They are protected.