I looked at her sharply, to see if she was joking, but she didn’t seem to be. She stooped, breaking off a twig and examining the dried-up centre. ‘How did you meet my dad?’

I reached for the corner of the water tank, trying to stop my legs shaking. ‘I just applied for a job to look after him. And I got it.’

‘Even though you weren’t medically trained.’

‘Yes.’

She considered this, flicked the dead stem away into the air, then got up, walked to the far end of the terrace, and stood, her hands on her hips, legs braced, a skinny Amazon warrior. ‘He was handsome, wasn’t he?’

The roof was swaying under me. I needed to go downstairs. ‘I can’t do this up here, Lily.’

‘Are you really frightened?’

‘I’d just really rather we went down. Please.’

She tilted her head and watched me, as if trying to work out whether to do as I asked. She took a step towards the wall, and put her foot up speculatively, as if to jump onto the edge, just long enough to make me break out into a spontaneous sweat. Then she turned to me, grinned, put her cigarette between her teeth and walked back across the roof towards the fire escape. ‘You won’t fall off again, silly. Nobody’s that unlucky.’

‘Yeah. Well, right now, I don’t really want to test the odds.’

Some minutes later, when I could make my legs obey my brain, we went down the two flights of iron steps. We stopped outside my window when I realized I was shaking too much to climb through and I sat down on the step.

Lily rolled her eyes, waiting. Then, when she grasped I couldn’t move, she sat down on the steps beside me. We were only, perhaps, ten feet lower than we had been, but with my hallway visible through the window, and a rail on each side, I began to breathe normally again.

‘You know what you need,’ she said, and held up her roll-up.

‘Are you seriously telling me to get stoned? Four floors up? You know I just fell off a roof?’

‘It’ll help you relax.’

And then, when I didn’t take it, ‘Oh, come on. What – are you seriously the straightest person in the whole of London?’

‘I’m not from London.’

Afterwards, I couldn’t believe I had been manipulated by a sixteen-year-old. But Lily was like the cool girl in class, the one you found yourself trying to impress. Before she could say anything else, I took it from her and had a tentative drag, trying not to cough when it hit the back of my throat. ‘Anyway, you’re sixteen,’ I muttered. ‘You shouldn’t be doing this. And where is someone like you getting this stuff?’

Lily peered over the railing. ‘Did you fancy him?’

‘Fancy who? Your dad? Not at first.’

‘Because he was in a wheelchair.’

Because he was doing an impression of Daniel Day-Lewis in My Left Foot and it scared the bejaysus out of me, I wanted to say, but it would have taken too much explaining. ‘No. The wheelchair was the least important thing about him. I didn’t fancy him because … he was very angry. And a bit intimidating. And those two things made him quite hard to fancy.’

‘Do I look like him? I Googled him but I can’t tell.’

‘A bit. Your colouring is the same. Maybe your eyes.’

‘My mum said he was really handsome and that was what made him such an arsehole. One of the things. Whenever I’m getting on her nerves now she tells me I’m just like him. Oh, God, you’re just like Will Traynor.’ She always calls him Will Traynor, though. Not “your father”. She’s determined to make out like Fuckface is my dad, even though he is patently not. It’s like she thinks she can just make a family by insisting that we are one.’

I took another drag. I could feel myself getting woozy. Apart from one night at a house party in Paris, it had been years since I’d had a joint. ‘You know, I think I’d enjoy this more if there wasn’t a small possibility of me falling off this fire escape.’

She took it from me. ‘Jeez, Louise. You need to have some fun.’ She inhaled deeply, and leaned her head back. ‘Did he tell you about how he was feeling? Like the real stuff?’ She inhaled again and handed it back to me. She seemed totally unaffected.

‘Yes.’

‘Did you argue?’

‘Quite a lot. But we laughed a lot, too.’

‘Did he fancy you?’

‘Fancy me? … I don’t know if “fancy” is the right word.’

My mouth worked silently around words I couldn’t find. How could I explain to this girl what Will and I had been to each other, the way I felt that no person in the world had ever understood me like he did or ever would again? How could she understand that losing him was like having a hole shot straight through me, a painful, constant reminder, an absence I could never fill?

She stared at me. ‘He did! My dad fancied you!’ She started to giggle. And it was such a ridiculous thing to say, such a useless word, faced with what Will and I had been to each other, that, despite myself, I giggled too.

‘My dad had the hots for you. How mad is that?’ She gasped. ‘Oh, my God! In a different universe, you could have been MY STEPMUM.’

We gazed at each other in mock-horror and somehow this fact swelled between us until a bubble of merriment lodged in my chest. I began to laugh, the kind of laugh that verges on hysteria, that makes your stomach hurt, where the mere act of looking at someone sets you off again.

‘Did you have sex?’

And that killed it.

‘Okay. This conversation has now got weird.’

Lily pulled a face. ‘Your whole relationship sounds weird.’

‘It wasn’t at all. It … it …’

It was suddenly too much: the rooftop, the questions, the joint, the memories of Will. We seemed to be conjuring him out of the air between us: his smile, his skin, the feel of his face against mine, and I wasn’t sure I wanted to do it. I let my head fall slightly between my knees. Breathe, I told myself.

‘Louisa?’

‘What?’

‘Did he always plan to go to that place? Dignitas?’

I nodded. I repeated the word to myself, trying to quell my rising sense of panic. In. Out. Just breathe.

‘Did you try to change his mind?’

‘Will was … stubborn.’