Mark wonders if Jon’s dealer misses his loyal servant now. If he even knows Jon’s dead. Or that it was his smack that killed him. Not that it was the heroin exactly, Mark remembers through his vodka fug. It was the clumsy draw, caused by the bitch forcing Jon to drink too much of Mark’s booze. But the smack played its part. If he hadn’t been jacking up, he wouldn’t be dead; that’s for sure.

He knows the address off by heart. He’s had the bit of paper Jon wrote it on for long enough, and he had to recite it to the guy with the bolt cutters only last week. Jon always insisted his dealer – Rudy – was a good guy, but that there was maybe a five per cent chance that things could turn nasty. Those were good odds, he’d explained, in the illegal drugs trade. But still, he liked someone knowing where he was.

Maybe he should go there now, Mark thinks, tell Rudy what happened to Jon. Not to blame him of course – that wouldn’t be clever – but to let him know. Just passing on information about a mutual friend. And if he manages to ignite a flicker of guilt, a momentary sense of remorse, that can’t be a bad thing. It’s about time the relentless ‘what if’ gnawed at someone else’s gut.

He pushes off the bench and pauses, giving his legs time to catch up with his brain signals. Then he drops the empty bottle of vodka in the bin, and heads back onto the street.

Ingrine House is an ugly 1960s tower block striped with dirty concrete slabs and lines of grimy windows, some lit up yellow but most in eerie darkness. Mark pauses outside. It feels like the whole place is screaming at him to stay the fuck away, but of course that’s just his imagination playing tricks, so he pushes on the main door to the block and keeps his head down as he trudges up the stairs. He feels a sudden urge to pee. Too much vodka, he decides, definitely not fear, because what has he got to be scared of? Rudy was Jon’s mate; he’ll be grateful for Mark stopping by. Mark sets his jaw, takes a breath and knocks on the flat’s peeling front door. It opens a couple of inches. ‘Yeah?’ a voice floats out.

‘Looking for Rudy,’ Mark says in a low voice, even though the communal hallway is empty. ‘I’m a mate of Clapham Jon’s.’ That’s what he was known as, not exactly imaginative. Mark waits a moment, then the door swings open. The bloke looks like a bouncer. His chest is wide and curved, and he’s wearing a thick gold chain around his neck.

‘In here,’ he says.