I often found myself wishing that Mum had had any reason at all to be at our school in 1999. If she had I might have been able to see her. But she didn’t, and so I couldn’t.

I ran to Beachview.

‘Ariel!’ he shouted, jumping up. He kind of hugged through me, and I shivered at the strange chill as his body vanished into mine. It was a bit like cold, and a bit like fizziness, a concentrated version of what happened when I walked down the corridors at school when they were filled with his people.

‘God, Joe,’ I said. ‘Yesterday, right? I’m so sorry. I just didn’t think.’

‘What happened?’ He was bouncing up and down. ‘I was so worried. I ended up … Well. Don’t laugh. I ended up lying on the floor, completely losing it. I thought something awful had happened to you. I thought you were ill, or you didn’t want to do this any more, or you’d decided it was all in your head. And then I realized that, without you, I’ll never be able to do anything except live this day over and over and over again, for all time. And it was the worst. Just the actual worst thing. The abyss, you know?’

I put my hand through his shoulder. I had to find out what had happened to him. Even if it didn’t change anything, at least then he would know.

‘I’m so sorry,’ I said again. ‘It wasn’t any of that. It’s just that it was Sunday, Joe. The mall closed at four. That was all. I didn’t think of it on Saturday, which was stupid because if I’d given it a moment’s thought I would have realized and then you wouldn’t have had to worry. I’ll never be able to see you on Sundays, but now we know that we can be prepared.’

I hesitated and then decided to carry on. ‘Joe, I missed you. It hasn’t been long, but I can’t imagine not being able to see you every day. Nearly every day. I’m kind of obsessed with working out what happened to you.’ I looked at him, slightly nervous of how exposed that made me feel, but Joe was laughing and crying at the same time, every bit as intense as me. ‘So I’ll never decide I don’t want to see you any more,’ I added, ‘because you kind of feel like my best friend.’

‘Ariel,’ he said. ‘You’re amazing, but I don’t want this to be too much pressure. Yesterday made me realize that, even though I’ve only just met you, I’m completely dependent on you. Like when someone’s sheltering someone in a war. Like Anne Frank. Or something.’

‘Hey,’ I said. ‘I’m not going anywhere, right? Friends?’