I psyche myself up for it by smashing a brick on the pavement and eating it. That proves that I’m not a human being: I’m a glitch and the rules don’t apply to me. My world really does feel like a computer simulation. I climb on to someone’s garden wall, take a few deep fake breaths and dive into their greenhouse as if I was diving into a swimming pool (a skill, I suddenly remember, that I used to have). My fingertips smash through the glass, but it doesn’t hurt. I land on my head on a wooden shelf of tomato plants, which all fall to the ground, covering it in leaves and soil and splinters of wood and shards of glass, but it doesn’t matter because they’re not real tomato plants, and it wasn’t a real greenhouse, and the glass is all fake glass. I stand up, note that I am completely unscathed, and jump back over the wall before some angry person comes running out to shout at me and make me pay for the damage.

Then, ready at last, I knock on the door of number twelve. The woman who answers has a baby on her hip and looks so much like Ariel that I think our time slip has done something weird and brought future Ariel into my timeline with her nephew. If time isn’t the static thing we thought it was, then anything’s possible.

No, though. This woman is in her twenties.

‘Hi,’ she says. ‘Can I help you?’

‘Oh my God,’ I say. ‘Yes, you can. You’re Anna Brown and this is Sasha, right?’

She takes a step back and her face closes.

‘I’m sorry,’ she says. ‘Should I know you?’

‘No, you shouldn’t. Sorry to turn up like this. I’m just so, so pleased I found you. My name’s Joe and I’m a ghost. This is a long and weird story, but I can prove it. I’m a friend of your other daughter, Ariel.’

She gives a half-smile, but takes another step away from me.

‘You’re a ghost,’ she says. ‘Right.’

‘Yes. I know a lot of things about you. I’m really sorry to do this. Hey, Sasha!’

Ariel’s mum turns to shield the baby from me. I realize that, even though this isn’t the real her, I can’t tell her that she’s going to die on 14 March 2018. I can’t tell her what I know about her husband.

‘Sorry, but you need to go,’ she says. I realize that I’m scaring her. I try to take a step back while keeping one foot inside the door, but she’s faster than me, and she pushes the door closed and shoves my foot right out. That would probably have really hurt if I had been able to feel it.