‘Ariel? Hi!’ Abby looked exactly like she did in her social-media photos. She was shorter than I’d expected, with bobbed brown hair and a nose sprinkled in freckles. She was wearing a flowery dress. ‘Thank you so much for coming over. Cup of tea? Or a cold drink?’ She held out a hand for me to shake. It was bony, delicate.

‘Tea would be lovely,’ I said, stepping into the house with a thrill. I’d done it. I was inside.

‘Come through to the kitchen. The girls are looking forward to meeting you. Well, Coco is. Zara’s very shy, but it’s nothing personal. She’ll be fine as soon as she’s got to know you. That’s why I needed to invite you over first really.’

I followed her into the house, which was a more stylish version of ours. The ground floor had been knocked together so there was a huge, bright yellow kitchen/sitting room/dining room with a pan of tomato sauce bubbling away, and a packet of spaghetti waiting on the side. A dark-haired girl ran straight up to me, curtseyed and said, ‘Hello. My name is Coco.’

I crouched down. ‘Hey, Coco. I’m Ariel.’

Abby laughed. ‘The curtsey is because she’s just started ballet. She’s very taken with it. We’re all supposed to curtsey to one other now.’

I stood up so I could curtsey to Coco, who laughed and flung her arms round my legs. This was going to be easy.

‘Are you a mermaid?’ she said into my leg. The very part of me, you’d have thought, that answered her question.

‘Only when I’m in water.’ I looked around for the other girl.

Zara was sitting in the corner of the sofa, wrapped in a blanket that she was using to hide her face. I turned to Abby, who went over to her.

‘Hey,’ she said, tapping her head. ‘Knock, knock! Zara. This is Ariel, remember? She’s going to look after you girls tomorrow when Daddy and I have to go to the work thing. We’ll be back home when you wake up in the morning. Just say hello.’

I walked over. ‘Hello, Zara,’ I said. ‘Hey, how old are you?’ She didn’t answer, so I said, ‘I’m sixteen. I bet you’re nearly sixteen too, aren’t you?’

The blanket moved. ‘Of course not,’ said a withering little voice. ‘Then I wouldn’t need to have a babysitter. I’m eight.’ Abby pulled the cover off her face, and I gasped.

She was Joe. Zara was exactly like her lost uncle, in a way that hadn’t come through in the Facebook photos. It was in the essence of her, the way she held her head, the way she smiled and looked down. He was right there, in her. Even her hair was like his, darker at the roots and light at the ends.