She shook her head. ‘No. He disappeared when he was still at school. They never found him, but they think he must have died.’

I realized that she was a small child and that she was supposed to be going to bed. This was terrible babysitting.

‘Maybe your uncle Joe and my mum are in heaven together,’ I said, and she gave me a sceptical look. ‘Perhaps they’re watching us now, talking about us because we’re talking about them.’

Zara nodded. ‘Yeah. They might be ghosts. They might be here right now. Sitting on the bed next to you. I hope so.’

I felt warm inside because she was closer to being right than she could possibly know.

‘I hope so too,’ I said.

When I tucked her in, I couldn’t help kissing her on the forehead like Mum used to do.

‘Night, Ariel,’ she said. ‘Night to your mummy Anna. Night to my uncle Joe.’

As soon as the girls were asleep, I set to work, digging deeper in my search for Troy Henry and Claire Simpson. Most of Joe’s friends and family had been easy to find: after everything Joe said about Lucas Ingleby I’d half expected him to be in prison, but he was, in fact, an accountant. Jasper Simpson’s name cropped up from time to time online and he had a private Facebook account. Claire and Troy had absolutely nothing.

I stopped when Izzy phoned.

‘Just checking in on you,’ she said. ‘There’s something different about you, Ariel. You know, you really can talk to me about anything any time.’ She paused, and it suddenly felt awkward between us. That never happened.

‘I’m OK,’ I said.

I imagined myself saying the next words, but it would hardly stop her worrying about me, so I didn’t add, I’ve got another best friend. You remember that boy who ghosted me? Well …

We had a strangely stilted conversation instead, and I ended it by pretending one of the girls had woken up.

I arrived home by taxi at half past eleven. Sasha was already in bed, and I popped my head into her room to wave at her, but my mind was spinning and I couldn’t sleep. I got out three big sheets of paper from my art folder and cleared a space in all the clutter on the table. I started to get down everything I knew so far.

PEOPLE FROM THE LAST DAY, I wrote on one, and I listed everyone we had discussed:

Joe’s dad, JASPER SIMPSON: Still alive, has a very small online presence. He seems to be in Devon, but impossible to find his address so far.

GUS SIMPSON: Contact established.

MR ARMSTRONG: a man called Thomas Armstrong died locally in 2004, aged 90 – possibly him.

TROY HENRY: Vanished without trace.

LUCAS INGLEBY: Accountant in London.

MARCO MANCINI: Music-vid/advert director, sometimes based in London, sometimes Italy, sometimes LA.