‘Puberty,’ said Charlotte when I was done.

‘What?’

‘Puberty,’ she said again. ‘Don’t tell me you don’t know what puberty means, Ashleigh.’

Of course I knew what puberty meant. It was just that I’d never thought of applying it to me or anyone else. Maybe I’d just assumed Aiden and I would stay kids forever.

‘It’s the start of the process whereby both girls and boys prepare for parenthood, turning from kids to adults …’

‘Yeah, Charlotte, I know …’ But I might as well have been trying to stop a runaway truck with an outstretched hand.

‘It all starts with gonadotropin-releasing hormones, which the hypothalamus secretes at the start of puberty. When that GnRH hits the pituitary gland, a pea-sized organ in the brain, then – bang – the chain reaction starts.’

‘Yes …’

‘Two more hormones are released in both males and females – luteinising hormone and follicle-stimulating hormone and these go to work on the body. In a boy they go to the testes …’

‘Please, Charlotte …’

‘… where they produce testosterone. In girls, however, they target the ovaries and produce oestrogen. Of course, all of this produces some dramatic changes in the bodies of both sexes.’

‘How do you know all this stuff, Charlotte? You’re like a walking textbook.’ I wasn’t going to stop her by conventional means, so I thought I’d appeal to her vanity. It worked.

‘I study,’ said Charlotte. She pointed to the sign above my head. ‘That’s the only way to create my future.’

‘Right,’ I said. I thought that maybe other things were more vital. Food and drink, for example. Breathing. But I decided to keep those thoughts to myself. ‘So you reckon these hormones are messing with Aiden’s head? That he’s started puberty?’

‘That’s my diagnosis,’ said Charlotte with what seemed like considerable satisfaction. ‘Hormones play havoc with emotions as well as bodily functions. We could get moody or depressed, become entirely unpredictable. Often parents think their kid has turned into some kind of monster …’

I zoned out then. Aiden had started puberty? It made sense, though happening pretty much bang on our thirteenth birthday seemed a coincidence. I thought about my own feelings, did a mental check of my body, but I couldn’t really detect any changes. Maybe my – what had Charlotte called it? GBH or some acronym? Maybe that hormone was on its way to my bits and I’d wake up tomorrow all hairy and grumpy. It was a disturbing thought.

Charlotte’s father didn’t turn up to dinner. In fact, I didn’t see him until the following morning when he drove us to school. So that evening, at eight o’clock sharp, we ate a limp salad with obviously fake chicken slices by ourselves. Her mother didn’t join us either. She put the food out on plates in front of us, smiled at me nervously and then bustled off somewhere. I was beginning to realise that in Charlotte’s household everyone was busy all the time. Maybe Charlotte’s comment about her dad wasn’t a joke. Maybe they did all work in their sleep.