‘I’m not going to judge you. I’m not going to report anything you say to anyone. I just … Well, you have to know that if you tell someone the truth, it will help. I promise. It will make things better.’

‘Says who?’

‘Me. There’s nothing you can’t tell me, Lily. Really.’

She glanced at me, then looked away. ‘You won’t understand,’ she said softly.

And then I knew. I knew.

Below us it had become oddly quiet, or perhaps I could no longer hear anything beyond the few inches that separated us. ‘I’m going to tell you a story,’ I said. ‘Only one person in the whole world knows this story because it was something I didn’t feel I could share for years and years. And telling him changed the whole way I felt about it, and how I felt about myself. So here’s the thing – you don’t have to tell me anything at all, but I’m going to trust you enough to tell you my story anyway, just in case it will help.’

I waited a moment but Lily didn’t protest, or roll her eyes, or say it was going to be boring. She wrapped her arms around her knees, and she listened. She listened as I told her about the teenage girl who, on a glorious summer evening, had celebrated a little too hard in a place she considered safe, how she had been surrounded by her girlfriends and some nice boys who seemed as if they came from good families and knew the rules, and how much fun it had been, how funny and crazy and wild, until some drinks later she realized nearly all the other girls had drifted away and the laughter had grown hard and the joke, it turned out, had been on her. And I told her, without going into too much detail, how that evening had ended: with a sister silently helping her home, her shoes lost, bruising in secret places and a big black hole where her recall of those hours should have been, and the memories, fleeting and dark, now hanging over her head to remind her every day that she had been stupid, irresponsible and had brought it all on herself. And how, for years, she had let that thought colour what she did, where she went and what she thought she was capable of. And how sometimes it just needed someone to say something as simple as No. It wasn’t your fault. It really wasn’t your fault.

I finished and Lily was still watching me. Her expression gave no clue to her reaction.

‘I don’t know what was – or is – going on with you, Lily,’ I said carefully. ‘It might be totally unrelated to what I’ve just told you. I just want you to know there is nothing so bad that you can’t tell me. And there is nothing you could do that would make me close a door on you again.’

Still she didn’t speak. I gazed out over the roof terrace, deliberately not looking at her.

‘You know, your dad said something to me that I’ve never forgotten: “You don’t have to let that one thing be the thing that defines you.” ’

‘My dad.’ She lifted her chin.

I nodded. ‘Whatever it is that’s happened, even if you don’t want to tell me, you need to understand that he was right. These last weeks, months, don’t have to be the thing that defines you. Even from the little I know of you, I recognise that you are bright and funny and kind and smart, and that if you can get yourself past whatever this is, you have an amazing future ahead.’

‘How can you possibly know that?’

‘Because you’re like him. You’re even wearing his jumper,’ I added softly.

She brought her arm slowly to her face, placing the soft wool against her cheek, thinking.

I sat back on the bench. I wondered if I had pushed it too far, talking about Will.

But then Lily took a breath and, in a quiet, uncharacteristically flat voice, she told me the truth about where she’d been. She told me about the boy, and about the man, and an image on a mobile phone that haunted her, and the days she had spent as a shadow on the city’s neon-lit streets. As she spoke she started to cry, shrinking into herself, her face crumpling like that of a five-year-old, so I moved across the seat and brought her in close to me, stroking her hair while she kept talking, her words now jumbled, too fast, too full, broken with sobs and hiccups. By the time she got to the last day, she was huddled into me, swallowed by the jumper, swallowed by her own fear and guilt and sadness.

‘I’m sorry,’ she sobbed. ‘I’m so sorry.’

‘You have nothing,’ I said fiercely, as I held her, ‘nothing to be sorry for.’

That evening Sam came. He was cheerful, sweet and casual in his dealings with Lily, cooked us pasta with cream, bacon and mushrooms, when she said she didn’t want to go out, and we watched a comedy film about a family who got lost in a jungle, a strange facsimile of a family ourselves. I smiled and laughed and made tea, but inside I simmered with anger I didn’t dare show.

As soon as Lily went to bed I beckoned Sam onto the fire escape. We climbed up to the roof where I could be sure I wouldn’t be heard, and as he sat down on the little wrought-iron bench I told him what she had told me in that spot, just a few hours earlier. ‘She thinks it’s going to hang over her for ever. He still has the phone, Sam.’

I wasn’t sure I had ever been so furious. All evening, as the television burbled in front of me, I had recast the last weeks in a new light: I thought about the times the boy had hung around downstairs, the way Lily had hidden her phone under the sofa cushions when she thought I might see it, the way she had sometimes flinched when a new message came through. I thought of her stuttering words – of the way she described her relief when she thought she had been rescued – and then the horror of what was to come next. I thought about the arrogance of a man who had seen a young girl in distress and viewed it as an opportunity.

Sam motioned to me to sit down, but I couldn’t keep still. I paced backwards and forwards across the roof terrace, my fists tight, my neck rigid. I wanted to throw things over the edge. I wanted to find Mr Garside. He came and stood behind me and rubbed at the knots in my shoulders. I suspected it was his way of making me stand still.

‘I actually want to kill him.’

‘It can be arranged.’

I looked round at Sam to see if he was joking, and was the tiniest bit disappointed when I saw he was.

It had grown chilly up there in the stiff night breeze and I wished I had brought up a jacket. ‘Maybe we should just go to the police. It’s blackmail, isn’t it?’

‘He’ll deny it. There are a million places he could hide a phone. And if her mother was telling the truth nobody is going to believe Lily over a so-called pillar of the community. That’s how these people get away with it.’