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 n.o.body is going to believe Lily over a so-called pillar of the community. That's how these people get away with it.'

'But how do we get that phone off him? She won't be able to move forward while she knows he's out there, while that image is still out there.' I was shivering. Sam took his jacket off and hung it around my shoulders. It carried the residual warmth of him and I tried not to look as grateful as I felt.

'We can't turn up at his office or her parents will find out. We could email him? Tell him he has to send it back, or else?'

'He's hardly just going to cough it up. He might not even answer an email that could be used as evidence.'

'Oh, it's hopeless.' I let out a long moan. 'Maybe she's just going to have to learn to live with it. Maybe we can convince her that it's as much in his interests to forget what happened as it is hers. Because it is, right? Maybe he'll just get rid of the phone himself.'

'You think she'll go with that?'

'No.' I rubbed my eyes. 'I can't bear it. I can't bear that he'll get away with it. That creepy, nasty, manipulative, limo-driving sc.u.mbag ...' I stood up and gazed out at the city below me, feeling briefly despairing. I could see the future: Lily, defensive and wild, as she tried to escape the shadow of her past.

That phone was the key to her behaviour, to her future.

Think, I told myself. Think what Will would do. He would not have let this man win. I had to strategize like he would. I watched the traffic creeping slowly past the front door of my block. I thought of Mr Garside's big black car, cruising the streets of Soho. I thought about a man who moved silently and easily through life, confident that it would always work his way.

'Sam?' I said. 'Is there a drug you could give that could stop someone's heart?'

He let that hang in the air for a moment. 'Please tell me you're kidding.'

'No. Listen. I've got an idea.'

She said nothing at first. 'You'll be safe,' I said. 'And this way n.o.body has to know a thing.' What moved me most was that she didn't ask me the question I had been asking myself ever since I outlined my plan to Sam. How do you know this will actually work?

'I've got it all lined up, sweetheart,' Sam said.

'But n.o.body else knows '

'Anything. Just that he's ha.s.sling you.'

'Won't you get in trouble?'

'Don't worry about me.'

She pulled at her sleeve, then murmured, 'And you won't leave me with him. At all.'

'Not for one minute.'

She chewed her lip. Then she looked at Sam, and over at me. And something seemed to settle inside her. 'Okay. Let's do it.'I bought a cheap, pay-as-you-go handset, called Lily's stepfather's workplace and got Mr Garside's mobile number from his secretary by pretending we had arranged to meet for a drink. That evening as I waited for Sam to arrive, I sent a text to Garside's number.

Mr Garside. I'm sorry about hitting you. I just freaked. I want to sort it out. L He left it half an hour before responding, probably to make her sweat.

Why should I talk to you, Lily? Y ou were very rude after all the help I gave you.

'p.r.i.c.k,' muttered Sam.

I know. I'm sorry. But I do need your help.

This is not a one-way street, Lily.

I know. Y ou just gave me a shock. I needed time to think. Let' s meet up. I'll give you what you want, but you have to give me the phone first.

I don't think you get to dictate terms, Lily.

Sam looked at me. I looked back at him, then began to type.

Not even ... if I'm a really bad girl?

A pause.

Now you've got my interest.

Sam and I exchanged a look. 'I just did a little sick in my mouth,' I said.

Tomorrow night then, I typed. I'll send you the address when I've checked my friend will be out.

When we were sure he wouldn't respond, Sam put the phone into his pocket, where Lily couldn't see it, and held me for a long time.

I was almost ill with nerves the next day, and Lily was worse. We picked at our breakfast, and I let Lily smoke in the flat, and was almost tempted to ask for a cigarette myself. We watched a film and did some ch.o.r.es badly, and by seven thirty that evening, when Sam arrived, my head was buzzing so much I could barely speak.

'Did you send the address?' I asked him.

'Yup.'

'Show me.'

The phone message was simply the address of my flat and signed L.

He had responded: I have a meeting in town and I'll be there shortly after eight.

'You okay?' he said.

My stomach tightened. I felt as if I could hardly breathe. 'I don't want to get you into trouble. I mean what if you get found out? You'll lose your job.'

Sam shook his head. 'Won't happen.'

'I shouldn't have pulled you into this mess. You've been so brilliant and I feel like I'm repaying you by putting you at risk.'

'We'll all be fine. Keep breathing.' He smiled rea.s.suringly at me, but I thought I could detect a faint strain around his eyes.

He glanced over my shoulder and I turned. Lily was wearing a black T-shirt, denim shorts and black tights, and she had done her make-up so that she looked simultaneously very beautiful and very young.

'You all right, sweetheart?'She nodded. Her skin, normally the slightly olive colour Will's had been, was unusually pale. Her eyes were huge in her face.

'It's all going to be fine, I'd be surprised if it takes longer than five minutes. Lou's been through it all with you, yes?' Sam's voice was calm, rea.s.suring.

We had rehea.r.s.ed it a dozen times. I wanted her to reach a point where she wouldn't freeze, where she could repeat her lines without thinking.

'I know what I'm doing.'

'Right,' he said, and clapped his hands together. 'Quarter to eight. Let's get ready.'

He was punctual, I had to give him that. At one minute past eight my buzzer rang. Lily took an audible breath, I squeezed her hand, and then she answered the entry-phone. Y es. Y es, she' s gone. Come up. It didn't seem to occur to him that she might not be what he thought.

Lily let him in. Only I, watching through the crack in my bedroom door, could see the way her hand trembled as she reached for the lock. Garside ran his hand over his hair, glanced briefly around the hallway. He was wearing a good grey suit, and tucked his car keys into his inside breast pocket. I couldn't stop staring at him, at his expensive shirt, his beady, acquisitive eyes as they scanned the flat. My jaw tightened. What kind of man felt ent.i.tled to press himself on a girl forty years younger than he was? To blackmail the child of his own colleague?

He looked uncomfortable, far from relaxed. 'I've parked my car out the back. Will it be safe?'

'I think so.' Lily swallowed.

'You think so?' He took a step back towards the door. The kind of man who sees his car as an extension of some minuscule part of himself. 'And what about your friend? Whoever owns this place.

They're not coming back?'

I held my breath. Behind me I felt Sam's steadying hand on the small of my back.

'Oh. No. It will be fine.' She smiled, suddenly rea.s.suring. 'She won't be back for ages. Do come in.

Would you like a drink, Mr Garside?'

He looked at her as if he were seeing her for the first time. 'So formal.' He took a step forward and finally closed the door behind him. 'Do you have Scotch?'

'I'll check. Come through.'

She began to walk to the kitchen, him following, removing his suit jacket. As they entered the living room, Sam walked past me out of the bedroom, strode across the hallway in his heavy boots and locked the inside door to the flat, placing the keys, jangling, in his pocket.

Garside, startled, turned and saw him, joined now by Donna. They stood there in uniform, against the door. He looked at them, then back at Lily, and faltered, trying to work out what was going on.

'h.e.l.lo, Mr Garside,' I said, stepping out from behind the door. 'I believe you have something to return to my friend here.'

He actually broke out in a spontaneous sweat. Until then, I hadn't known it was physically possible.

His eyes darted about for Lily, but as I had stepped out into the hall she had moved so that she was half behind me.

Sam stepped forward. Mr Garside's head reached just above his shoulder. 'The phone, please.'

'You can't threaten me.'

'We're not threatening you,' I said, my heart thumping. 'We would just like the phone.''You're threatening me just by blocking my exit.'

'Oh, no, sir,' said Sam. 'Actually threatening you would involve mentioning the fact that, if my colleague and I chose, we could pin you down right here and now and inject you with dihypranol, which would slow and ultimately stop your heart. Now that would be a threat, especially as n.o.body would question the word of the paramedic crew who had apparently tried to save you. And as dihypranol is one of the few drugs that leaves no trace in the bloodstream.'

Donna, her arms crossed across her chest, shook her head sadly. 'It's a shame, the way these middle- aged businessmen just drop like flies.'

'All sorts of health issues. They drink too much, eat too well, don't take enough exercise.'

'I'm sure this gentleman here isn't like that.'

'You'd hope not. But who knows?'

Mr Garside seemed to have shrunk by several inches.

'And don't even think of threatening Lily. We know where you live, Mr Garside. All paramedics have that information to hand if and when they need it. It's amazing what can happen if you p.i.s.s off a paramedic.'