‘It’s about a mile to my car. Can you make it?’ Knox asked him, knowing already that the answer would be no.

Knox peered through the gap in the door. Rush hour was just beginning and he could see a few people heading to the nearest tube station or bus stop. But no one looked like they were loitering, or paying well-disguised attention to the half-open door as they passed it.

‘Wait here,’ he said. ‘And don’t talk to any strangers.’

Knox stepped casually out into the street, as if he was simply leaving his office for the pub or to take the train home to the suburbs, then, when he was twenty yards from the doorway, he burst into a sprint.

He calculated he could get to his car and back in fifteen minutes. He’d have to be pretty direct, but that didn’t matter so much—if someone was waiting for them then they already knew where they were, and Knox could worry about losing them later when he and Williams were properly mobile. He also hoped that if someone was watching the doorway and saw him racing away from it they’d be more likely to follow him than go and see what had happened all the way down in the store.

In the end it took almost twenty minutes for Knox to run down Little Britain, through Postman’s Park and its memorial to people who died saving the lives of others, and along London Wall to where he’d left his Jaguar, then drive back to Smithfield.

By the time he pulled up in front of the doorway and Williams slipped into the passenger seat, and almost immediately fell asleep, Knox had decided where he was going to take him—the only place he could take him.

As they drove through the early-evening traffic, and started to wend their way up to the old, rich hill that stood over the north of the city, Knox tried to process what had just happened and found that he couldn’t. Williams had brushed off his apology, then apparently forgotten their conversation had even taken place as he quickly and coldly killed two men. And now he was sleeping peacefully next to him, seemingly without a care in the world.

Williams was unconscious, but he wasn’t asleep. Sleep would have meant rest, recovery, rejuvenation. Williams was denied all of that. The exhaustion that had pulled him out of the chaos and confusion of the waking world had only dragged him down into something much worse.