‘Very good!’ Mr Flint calls out, halting us before I can work out what I did or whether I can do it again.

The acorn at my throat is uncomfortably warm, and I’m fairly sure it did something in there.

‘Let’s change. Excellent defence work, Stella – not at all bad for your first time. Let’s have you out. Tash, you’re getting pretty nifty with those needles – though you need to remember not to rely upon them alone. It is your power that drives them, not the other way around!’

He calls Yanny up to face Tash next, and he’s pretty excellent at the fight. His smoke lingers in the air, and he has a fiery whip that curls around his wrist and snaps in the air. Mr Flint pits student after student against him, but nobody stands for long, until another girl – Laurel – steps in, and they parry with hot words and quick, dancing feet, his whip against the nimble flick of her slim wooden staff, until finally Yanny holds up his hands in defeat – through tiredness if nothing else, by the look of him.

‘You spread yourself too thin, boy!’ Mr Flint snaps from the sidelines. ‘You need to control it better; rage will only carry you so far!’

Yanny nods, tight-lipped, as we’re dismissed.

‘Are you OK?’ I ask him once the lesson is over, while he fixes his glamour out in the corridor. I can feel the stretch of magic in the air, it’s thin, dangerous.

‘Yep,’ he says, rolling his shoulders as we step through the wooden door and head down the stairs.

‘That was intense.’

He shrugs. ‘Yep.’

I don’t know what to say, how to make him feel better. He looks utterly worn out, and there’s a tension around him that makes me anxious. I guess there’s probably nothing I can do right now.

I keep close though, all morning, and Zara senses something too. She doesn’t comment, but I know she’s worried. We get through double English, and then it’s maths, and the winter sun streams through the windows, making patches of searing light across the desks. The radiators are on full blast, and Yanny is struggling, his skin pale beneath bright freckles. I whisper the words of heart, to lend him strength – and for a while, it seems to work. He picks up his pen, fixes his attention on the page before him. But as soon as I’m done with the spell, his hand stills, and he wilts back into the chair.

‘Yanny –’ Zara leans into him – ‘concentrate.’

He sits upright and pulls the book closer.

‘Here,’ she says, shaking her head as she flips the pages. ‘That one. Look, I’ll help you with it later. Just look busy for a minute – Mr Goodenough is on the warpath.’

And he is, his blue eyes flashing around the classroom as if looking for a target. Yanny bends low over his book, as if deep in study, but his eyes are unfocused. Zara frowns over at me.