She gets up to go to the toilet, not because she needs to but because she can’t lie still another second. The corridor is dim and even hotter than their room. Holly is halfway down it and thinking cold water when the shadow of a doorway convulses, only a foot or two away. She leaps back against the wall and grabs a breath ready to yell, but then Alison Muldoon’s head shoots open-mouthed out of the shadow, vanishes in a burst of urgent squeaky noises, and pops back out again.

‘Jesus!’ Holly hisses. ‘You almost gave me a heart attack! What is your problem?’

‘OhmyGod, it’s you, I thought— Jo!’ And she’s gone again.

By this point Holly is getting curious. She waits and listens; the rest of the corridor is silent, everyone deep under the weight of the night.

After a minute Joanne appears in the doorway, frizz-haired and wearing pale-pink pyjamas that say ooh baby across the chest. ‘Um, that’s Holly Mackey?’ she snaps, examining Holly like something in a display case. ‘Are you retarded or what? I was asleep.’

‘Her hair,’ Alison bleats, just above a whisper, behind her. ‘I just saw her hair, and I thought—’

‘OhmyGod, they’re both blond, so is like everybody? Holly doesn’t look anything like her. Holly’s thin.’

Which is the biggest compliment Joanne knows. She smiles at Holly, and rolls her eyes so they can share a laugh at how thick Alison is.

The thing about Joanne is you never can tell. Today she could be your snuggled-up best friend, and she’ll get all wounded if you don’t play along. It puts you at a disadvantage: she knows who she’s dealing with; you have to figure it out from scratch, every time. She makes Holly’s calf muscles go twitchy.

Holly says, ‘Who did she think I was?’

‘She came out of the right room,’ Alison whines.

‘Which means she was going the wrong way, duh,’ Joanne says. ‘Who cares if she goes to the loo? We care if she goes out. Which, hello, is that way?’ Alison chews a knuckle and keeps her head down.

Holly says, ‘You thought I was Selena? Going outside?’

‘I didn’t. Because I’m not retarded.’

Holly looks at Joanne’s tight face, too hard for the cutesy pyjamas, and it occurs to her that Joanne is kicking Alison because she’s some strange combination of relieved and disappointed. Which is crazy. She says, feeling her way, ‘Where would Selena be going?’

‘Don’t you wish you knew?’ Joanne says, tossing Alison a smirk. Alison lets out an obedient sharp giggle, too loud. ‘Shut up! Do you actually want to get us caught?’

Holly’s heartbeat is changing, turning deeper and violent. She says, ‘Selena doesn’t go out on her own. Only when we all do.’