He started counting people off on his fingers. ‘Are these people all on your list? Dad and Gus, of course. Troy Henry. The neighbour, Mr Armstrong. Jemima. I think I see the back of Marco’s head some days. There’s Alicia, Lucy. Lucas Ingleby.’

I nodded. We’d been over these names several times now. All his old schoolfriends were living regular lives in Devon or London, apart from Troy who seemed to have vanished altogether.

I wrote down Joe’s teachers’ names: as far as we could work out only the benign Mr Patel taught us both. The most significant one on Joe’s last day was Mrs Dupont because of the upcoming trip, but neither of us thought she was about to burst into this room and murder him.

‘Dad fancies Mrs Dupont,’ he said, and told me a story about his dad flirting with her at a meeting. It was rare for him to remember things from twenty years ago so clearly, so it must have made an impression.

I had to work very, very, very hard to play it cool when Gus opened the door because he was Joe’s brother and I wanted to tell him everything straight away.

‘Hi,’ I said. ‘I’m Ariel, the babysitter.’

‘Ariel!’ He grinned and gestured for me to come in. His face was lined in a gentle way because he was thirty-seven and he’d lost his brother. ‘Thanks so much for coming. I’ve been hearing about you from the girls. You made an impression. Good to meet you.’

I followed him inside. Gus was taller than I’d expected, and he looked, of course, exactly as he had when I’d spied on him the other day. I wished so much that Joe could have come here with me.

‘Your girls are lovely,’ I said, nerves making me talk fast. ‘It was so nice to meet them. I think we’ll have a good time together. I’m going to be an aunt in July, so it’s nice to spend time with children. You know. Get used to not being the youngest any more. I’ve always been the youngest in my family.’

I was babbling, trying to seem friendly. I wanted to be someone they could talk to, to tell Gus things so that he might tell me things back.

‘A little niece or nephew!’ Gus looked mildly interested. ‘That’s nice. First one?’

‘Yes,’ I said. I took my phone out of my pocket, looked at it and pantomimed relief. This was shit, but it was the only plan I had. ‘Oh phew. Sorry. My friend got hit by a car yesterday, just really mildly, but she had to go for a check-up today. And it’s all fine.’

The girls were watching TV, and Abby was rushing around in a fog of perfume, wearing a wrap dress and sparkly earrings.