‘This is nice,’ Izzy said. ‘Isn’t it? A day trip to London. You know what? You’re mad, but I want to find out what happened to your boy too. Those little girls were so adorable. Their poor dad!’ She shivered. ‘If we can help that family then bring it on. I mean, I can’t have you going to track down a suspect alone, can I?’

Before we knew it we were passing through Reading and I did a namaste hand thing in what I thought might be the direction of the long-defunct Yoga Dojo. Half an hour after that we were in London.

It was warmer than it had been at home, and there were trees with pink cherry blossom at the top of Lucas Ingleby’s road in Haggerston. The sun warmed my cheeks as we walked slowly up to the door of his block of flats. I looked at Izzy, who was clearly regretting the trip now we were actually about to doorstep a strange older man. I could practically see the thought bubble above her head saying, I could be with my girlfriend. I was getting psyched up to find the right buzzer when the front door opened.

He went to walk past without even looking at us, but I stepped into his path.

‘Hi,’ I said, trying to equate this muscular man with the Lucas Joe had told me about, the boy I’d seen in the corridor. His hair was flecked with grey, and that was a jolt, because even though Gus was old too he was Joe’s big brother, while this man was in Joe’s year at school. They were pretty much exactly the same age. If Joe had lived he might have been going grey too. Instead he was younger than me.

Also, I’d seen this man as a boy very recently, and that was enough to freak me right out. I had heard him talk, watched his hurt face when Joe was unthinkingly cutting.

He stopped. ‘Hi?’ he said, neither friendly nor unfriendly. He was just a man who was walking down his own street on a Saturday afternoon. On his way to the gym, judging by his clothes and bag.

‘Lucas?’ I said. ‘This sounds weird, but could we talk to you for a minute? We’re from your old school and we’re writing a thing about Joe Simpson for the school magazine. Because it’s twenty years since he disappeared. His brother, Gus, said you used to be friends with him. Do you have a couple of minutes to talk?’