Miss Niven was taking them through the steps for differential calculus, substitute x for x+h, subtract the original equation, single out h by algebra and the rest. Tyler would normally soak this up, immerse himself in the abstract world, but he couldn’t get into it. He was only a third of the way through the exercise when the bell went. He shuffled his stuff together and pushed it into his bag, then headed outside for morning break.

Connell was waiting at their usual corner with another kid, Ahmed from his reggie class. They were talking about a girl Ahmed fancied from the year below, how he was planning to get in there. Tyler checked his phone alerts, a few dull Instagram posts, some Hibs gossip. Then he checked the local news and froze. Clicked through to the story and scanned it, his heart thudding.

The Holts were offering a ten-grand reward for information on the stabbing. Ten fucking grand. That was an insane amount of money, but of course Deke had plenty. Tyler had seen his house. There were just four paragraphs to the story, most of it recapping the original break-in and stabbing. It referred to Deke as Derek, a ‘devoted husband and father’, and mentioned Ryan too. It also gave details of Monica’s car, the Audi, identifiable by its personalised number plate.

‘Hey, man, you all right?’ Connell said. He looked at Tyler’s phone screen over his shoulder, took in the story.

‘Ten grand,’ Connell said. ‘Holy shit, I could use some of that. I don’t suppose you’ve heard anything?’

Tyler stared at him. ‘Of course not.’

Connell held his hands up. ‘Just asking.’

Tyler thought about the shotgun under the bed, then about Monica’s car, which they’d fenced to Wee Sam. He must’ve realised whose car it was by now. And all the stuff from the Holt house Barry had already sold. How many people did that involve? A lot of them would’ve sussed it. Some of them might’ve kept quiet to avoid getting involved, but now there was ten grand in the mix.

He looked around. A gang of younger boys were hunched over their phones in a corner. A bunch of girls in tight leggings and with sculpted eyebrows were taking selfies while smoking. The nicotine drifted to his nostrils and he was reminded of his mum. What that was doing to Bean’s lungs in the house. They learned about that stuff in primary school. Bean asked about it at home one day and got the back of Angela’s hand in response. It was the one time Tyler had been aggressive with his mum, hauling her off Bean and throwing her onto the sofa in the living room. He could take all the shit she threw at him, but not at his sister.

He had to tell Barry about the reward. He moved away from Connell, who raised an eyebrow, and called his brother’s mobile. It rang five times, then Barry on voicemail, Ant and Dec barking in the background. He hung up. He looked around again, waiting for Ryan Holt or his dad to appear from nowhere and stab him. He realised he’d been chewing the inside of his cheek, so he released his bite. The flesh was raw. He poked his tongue at it.

He shook his head and turned to leave.

‘Hey.’ Connell behind him. ‘What about geography?’

Tyler just kept walking out of the school gates and down the road.

The dogs were barking before he knocked on the door. Sometimes, when they weren’t locked away in the bedroom, they’d start before Tyler had even got out of the lift, like an alarm, letting Barry know when anyone appeared on their floor. The doorbell didn’t work, ever since Barry ripped the wiring out as part of his campaign to get rid of the Syrian family. Tyler rapped on the door and the dogs got louder. He could hear one of them slavering against the door, scratching at the paintwork. Barry must not have fed them. He did that sometimes as a training method, to make them angry and mean, more savage in the build-up to a fight.

There was a place out near Tranent, off the A1 at Carberry, where someone had dug a pit in the woods and filled it with concrete. Barry would take the dogs to fight. There was so much dead space in East Lothian it was easy to get away with stuff like that. This place was between a golf course and a historic mansion, farms and fields all around, and nobody gave a shit. Either that or they were too scared to confront anyone. Barry and Kelly had taken Tyler out there a few times years ago with a previous pair of dogs, now dead. It was like an initiation to toughen him up. He’d endured the spectacle a couple of times, the amphetamines for the mutts beforehand, the tweaking of bollocks and injections to give their dogs the edge, the lacerated throats and savaged ribcages, bones and sinew showing, raw muscle like webbing exposed beneath fur. It was intended to shock but Tyler was already close to unshockable. But he hated it all the same and made himself sick once in front of everyone. It earned him a beating, but Barry had been so ashamed at the mocking he got from the other knuckleheads that he left Tyler at home after that.

Still no one had answered the door. Tyler went to open it, but the jaws of Ant or Dec were immediately at the crack in the door, slobbering and fighting to get at him.

‘Down.’

He could make out Kelly yanking on the dog’s collar, heaving it away from the door and into the kitchen, where she shut it in. She came back and opened the door. She was wearing black shorts and an oversized pink sweatshirt with Awesome scrawled across it. She looked tired and her hair was greasy, a sheen of coke sweat on her face.

‘There’s a reward,’ Tyler said.

‘What?’

‘Ten grand for information on the stabbing.’

‘Shit.’

‘Is Barry around?’

Kelly shook her head.

‘Where is he?’

Her head went down. ‘I don’t know.’

Tyler’s heart quickened for a moment. ‘You think something happened to him?’

Kelly shifted her weight. ‘Like what?’

‘Like the Holts found him.’

‘Nothing like that.’

‘But you said you don’t know where he is.’

‘He’s with Cherise.’

This was Barry’s ex, who took out a restraining order on him years before but forgot about it when she was drunk and it suited her. And Barry would run back. Cherise didn’t seem to mind that Barry was shacked up with his own sister the rest of the time. And Kelly was too weak to complain about it either. What a fucking mess.

‘Kelly, what are you doing?’

Her face hardened at his tone. ‘What do you mean?’

‘You know what I mean.’

She stuck her chin out. ‘Shouldn’t you be in school?’

Tyler could still hear that dog in the kitchen, and he wondered where the other one was. Maybe they would kill each other, and they’d all get some peace.

‘I came to tell Barry about the money. We’re fucked now, you realise that?’

‘No one will grass.’

‘Of course they will, it’s ten grand.’

‘So what?’

‘Just tell Barry and see what he says. Hope he doesn’t shoot the messenger.’

He turned to go into his own flat, leaving her standing in the doorway.

‘Tyler, wait.’

Something in her voice made him stop and turn.

She looked scared. That was pretty common around Barry but Tyler couldn’t remember the last time he’d seen her like this. She placed a trembling hand against her forehead, through her hair, back to her face.

‘What is it?’ Tyler said, stepping back towards her.

‘Nothing, I just…’

Tyler stood watching her.

‘I can’t sleep,’ Kelly said, her head lowered, eyes darting. ‘I keep picturing that woman in the house.’

Tyler sighed. ‘I know.’

Kelly scratched at the doorframe. ‘Why did Barry have to stab her?’

‘Why does Barry do anything? Because he’s Barry.’

Kelly shifted her weight. ‘He’s not all bad.’

Tyler couldn’t believe what he was hearing. ‘Kelly, stop kidding yourself.’

‘There’s another side to him, Tyler, you wouldn’t understand.’

That got Tyler mad. ‘Are you insane? He’s treated us both like shit our entire lives. He’s a bully and a psycho and now he’s going to get us killed.’

‘There’s stuff you don’t know,’ Kelly said.

‘Like what?’

Kelly took a deep breath, raised her head. ‘He protected me.’

‘From what?’

Kelly swallowed. ‘Back when we used to stay with Dad. Years ago. Dad would come in from the pub hammered, come to my room. Wake me up, you know.’ She picked at an invisible splinter in the doorframe. ‘He would do things. And hit me too. But one time he did it, Barry came in with a kitchen knife and held it to his bollocks, said if he ever touched me again he’d lose them. It was the first time I ever saw Dad scared.’

‘Christ,’ Tyler said. ‘Why did you never tell me this before?’

Kelly shrugged. ‘I’m telling you because I want you to understand that Barry has always looked after me. And he’ll look after us now, I’m sure of it.’

So Kelly had gone from being abused by her dad to sleeping with her brother. Tyler remembered once when Bean was a baby, he’d come home from school and found Kelly lying on the floor in the living room playing with her. She’d made a nest out of dirty cushions for Bean to lie in, and a wobbly mobile out of the taped-together bits of a ripped-up cardboard box, which Bean was swiping and giggling at. Kelly had looked embarrassed to be caught caring, but she didn’t stop. Half an hour later Barry came in stoned off his tits and ripped the mobile apart.

Why couldn’t she see he was fucking toxic? It was so obvious to Tyler, to everyone surely. But she couldn’t see his manipulation for what it was, she thought she was standing by the man who looked after her.

‘He can’t protect us anymore,’ Tyler said. ‘Not from this.’

‘Of course he can, he’s Barry.’

‘He’s losing the plot. You saw him last night. That burglary job was nuts, he was looking for a fight, he wanted to get caught.’

Kelly shook her head. ‘We just need to keep our heads down. Keep out of trouble.’

‘And you think Barry’s capable of that?’

Kelly nodded but it wasn’t convincing.

Tyler narrowed his eyes. ‘Maybe there’s another way.’

‘How do you mean?’

Tyler tried to think it through before he spoke. ‘That woman in the hospital, she could die. Then it’s murder. We didn’t stab her, neither of us. The police are sniffing around, and there’s a reward now. Maybe we just tell the truth.’

Kelly’s eyes widened. ‘We can’t do that.’

‘Why not?’

‘We just can’t.’

‘We don’t owe him anything, Kelly. He would sell us out without even thinking if it was the other way round.’

‘No way.’

‘He would.’

The look on Kelly’s face hardened. ‘If you grass on him, Tyler, he’ll kill you.’

That was true and Tyler knew it. And still Kelly couldn’t see what kind of brother that made him, like the two parts of her brain were disconnected from each other.

Tyler shook his head and stepped away.

‘Tyler,’ Kelly said as he reached his own door. ‘We have to stick together.’

He didn’t turn back, just got his key out and opened the door to his flat.

The smell hit him, something more than the usual stale booze and fags. It was shit and piss, and a sweet undercurrent of something rotten. He walked into the living room and the smell got stronger so that he had to hold the crook of his arm over his nose. Then he saw Angela on the floor. She was naked and he could see track marks on her arms and legs, open sores that pockmarked her body like craters. She had the ligature still tight around her upper arm and the lower part of the arm was dark blue, like the edge of a summer night. Her face was a paler blue, scabbed lips white. He noticed a runny shit staining her buttocks and leaking onto the carpet.

He ran over and loosened the belt from her arm, the marks from the buckle springing up white underneath, her skin slow to return to normal. He held a hand over her mouth and knelt there for a few seconds. He couldn’t feel any breath. He did the same under her nose, nothing. He dug two fingers into the sinew at her neck and tried to imagine a pulse. He closed his eyes to concentrate better. He thought he felt something but wasn’t sure. He tried to calm his breath, his own heart racing against his chest, the adrenaline rising up in him.

‘Come on,’ he said to himself.

He pushed his fingers in harder against the neck muscle so that he could feel her voicebox. He imagined ripping it out, then felt a low murmur, a throb against his fingertips. A pulse, definitely a pulse. But then nothing for a second or two, then maybe another beat.

‘Fuck’s sake.’

He took his fingers from her throat, grabbed her shoulders, lifted her and shook. Her neck was loose, her head lolling like it might come off.

‘Wake up,’ he said, and slapped her across the face. Her head offered no resistance, just flipped across, lank hair falling into her eyes.

He looked around the room for an answer – just unwashed dishes in the sink, fag ash and heroin gear on the carpet. The stench was making his eyes water.

He dropped her on the floor, her head landing with a thunk.

He pulled out his phone and called 999, got put through to the ambulance service, but when he explained it was a suspected overdose and gave the address there was a pause, estimated arrival time was forty-five minutes. She would be dead in forty-five minutes and they both knew that.

He hung up and ran to the other flat, thumped his fist on the door.

‘Kelly.’

He heard the dogs then Kelly opened the door.

‘It’s Mum, she’s OD’d again,’ he said.

‘Seriously?’

‘Come on.’

‘Have you called an ambulance?’

‘They said three quarters of an hour. She’ll die before they get here. Is Barry’s car downstairs?’

Kelly shook her head. ‘He took it to hers.’

Tyler took Kelly’s arm and dragged her to his flat, into the living room. She put a hand over her nose. ‘The fuck?’

She took in the scene for a few moments. ‘Call a taxi.’

‘You know they won’t pick up from here.’

‘Any bright ideas?’

Tyler looked at his watch, half twelve, lunchtime. He thought about Barry holding him in the water last night, what he’d told him. But he didn’t have any other option.

He dialled and she answered. ‘Hey, what’s up?’

‘I need a favour.’