Sister Cornelius is being cuboid and grim in front of the door; Miss Long is off down the other end of the hall, unsticking Marcus Wiley from Cliona, who looks like she’s not sure which of them she hates more. Sister Cornelius gives Julia and Finn a suspicious glare. Julia smiles back. ‘The punch is lovely,’ she shouts, raising her cup. Sister Cornelius looks even more suspicious.

Julia puts her cup down on a windowsill. Out of the corner of her eye she sees Finn, who apparently catches on fast, do the same thing.

Becca falls over. Sister Cornelius gets a wild missionary look and charges off down the hall, shoving dancers out of her way right and left, to interrogate Becca and breathalyse her and run tests for Young People’s Drugs. Holly will deal with her, no problem; grown-ups believe Holly, maybe because of her dad’s job, maybe just because of the total sincere commitment she puts into lying. ‘Go,’ Julia says, and zips out of the door, hearing the slam behind her a split second later but she doesn’t look round till she’s down the corridor and into the dark maths room and the footsteps echoing behind her turn into Finn swinging around the door frame.

Moonlight stripes the room, tangles confusingly in chair-backs and desk-legs. The music has turned into a distant hysterical pounding and shrieking, like someone has a tiny Rihanna locked in a box. ‘Nice,’ Julia says. ‘Shut the door.’

‘Fuck,’ Finn says, banging his shin off a chair.

‘Shh. Anyone see us go?’

‘Don’t think so.’

Julia is unscrewing the window-bolt, moonlight slipping over her fast-moving hands. ‘They’ll have someone patrolling the grounds,’ Finn says. ‘Or anyway they do at our dances.’

‘I know. Shut up. And get back; you want to get seen?’

They wait, backs against the wall, listening to the small tinny shrieking, keeping one eye on the empty sweep of grass and one on the classroom door. Someone’s forgotten a uniform jumper, squiggled down the back of a chair seat; Julia grabs it and pulls it on, over her polka-dot dress. It’s not exactly flattering – it’s too big and it has boob dents – but it’s warm, and they can feel the outdoors cold striking through the glass. Finn zips up his hoodie.

The shadows come first, sliding around the corner of the boarders’ wing, long on the ground. Sister Veronica and Father Niall from Colm’s, marching side by side, heads whipping back and forth while they scan every inch of cover.