‘We’ve been worried about Aiden too, Ash,’ she said. ‘I won’t lie to you. You’re not the only one to have noticed the changes in his temperament. He’s always been such a … predictable child. You could rely on him one hundred per cent. But now … well, he’s rather difficult, to be honest. His behaviour is … unexpected.’

‘Charlotte said it was probably puberty. Hormonal changes. That would account for it, wouldn’t it?’

Mum raised her eyebrows. ‘Oh, you’ve talked to Charlotte about this, have you? That tells me a lot about how worried you are. Yes, puberty would explain it, but so would the head trauma he suffered on camp. And his mood switches started immediately after that. So I think you’re right to be concerned, Ash. I really do.’

‘But he’s going to be okay, isn’t he?’

Mum smiled and patted my leg.

‘I’m sure he is,’ she said. ‘You know that your father and I will spare no expense – and that clinic is expensive – to get Aiden back to the way he was.’

‘Oh, I don’t want him the way he was, Mum,’ I said. ‘He’s much more interesting now. Before, he was … well, you said it. Predictable. I’ve always loved Aiden, but now I like him as well. Do you know what I mean? I’m all good with unpredictable, I just don’t want him to be ill.’

Zorro started being a very bad dog indeed and this helped with Aiden’s recovery.

A couple of days after he came back from the clinic, we both went for a swim. As always, Z paced along the sides of the pool while we did laps. He’d stopped jumping in and now appeared to be a little scared of the water. According to Mum that’s because he was learning. ‘A baby will have no problems with water’, she said. ‘But later it will learn to associate it with danger. That’s why it’s good to teach a baby to swim before it becomes scared. Leave it too long and then you have to train it to overcome the fears it’s developed in the meantime.’ Z, it seems, was employing something Mum called ‘deep learning’ to have a healthy worry about drowning, even though it was physically impossible for him to drown.

Anyway, Aiden and I were chatting after a few laps and we noticed that Z had disappeared. Aiden tried whistling, but he didn’t reappear. After a few minutes we forgot about him entirely. I was asking my brother about the clinic. It had never really interested me before, but now I realised that the whole place, and what happened there, was a complete mystery.

‘So what are your doctors like?’ I asked. ‘And the nurses?’