Five minutes later, I was satisfied.

“Okay,” I said quietly. “Let’s go.”

Michael Johnson had a flat in a tower block. It turned out to be one of three, angled so that the blank windows and empty balconies twenty stories above faced each other across a forlorn spread of dirty tarmac. We parked outside Johnson’s block. There were large gray bins in a wire-mesh cage by the entrance, but one of them had been tipped over onto its side, and litter was skittering aimlessly across the ground in the breeze. An old set of double doors led inside, the glass there dark.

Sarah leaned forward and peered up dubiously.

“I’m guessing eight twelve means he’s on the eighth floor?”

“Probably,” I said. “The lift might be working.”

“If not, at least we’ll get our steps in.”

I turned the engine off, and we sat there for a few seconds in silence. Outside the car, there didn’t seem to be anybody else around at all. The world was so quiet that the tower block in front of us now felt eerie and deserted.

“You realize we might be doing something very stupid?” Sarah said.

“I’ve been thinking that ever since we left the house.”

She nodded to herself. “As long as we’re on the same page.”

Then she leaned back and clicked her seat belt off.

We walked across to the block. The entrance doors opened onto a drab corridor that led down to a claustrophobic hall, with narrow stairwells disappearing up on three sides. There were two lifts, one of them working. I pressed the call button and we waited, the half reflection on the swirled metal of the doors turning us into a pair of distorted ghosts. The interior was small and cramped, with torn linoleum on the floor and undecipherable graffiti daubed across the misty mirror. The elevator lurched as it set off and then juddered more alarmingly with every floor we passed.

“We’re going to die,” Sarah said.

“It’ll be okay.”

“I don’t want to die in a lift.”

We reached the eighth floor and then followed the corridor around. There was no natural light, and a number of the strips above us weren’t working, so we passed through pockets of shadow. All the doors were shut, but I could hear television programs and music through the thin wood. A couple arguing. A baby crying.

We reached flat 812.

I knocked on the flimsy door. There was no immediate response from inside the flat, and Sarah and I shared an uneasy glance. There could have been a hundred reasons why Michael Johnson wasn’t home right now, and most of them were innocent. But I could tell that we were both focusing on the one that was not.

Then I heard careful movement on the other side of the door.

A few seconds later it opened a crack, a chain holding it in place, and a man peered out at us. Assuming this was Michael Johnson, he was only six or seven years older than us, but time had not been kind to him. Even from the little I could see through the gap, his eyes were bleary and his face was pale and drawn. He was wearing a dirty, baggy T-shirt, and a sagging gray beanie in which his head appeared almost lost.

“Michael Johnson?” I said.

“Who are you?”

He sounded suspicious. But I thought there was also an undertone of fear. Once again, there were many possible reasons for that, but I couldn’t help imagining the worst.

“My name’s Daniel,” I said. “This is my friend, Sarah.”

“Are you police?”

“No. I’m a doctor. Sarah’s a… singer.”

He looked at Sarah then back at me.

“What do you want?”

How would my father approach this? As far as he had taken his own investigation, I didn’t imagine he would have found his way here.Michael Johnsonwas too common a name to pin down, and I was sure that the method Sarah had used to find this address would never have occurred to him. But if he had done, what would he say? What words would he have used to persuade a frightened man to unchain the door and talk to him?