‘Gemma saw them out in the grounds by accident the first time, like a week before – she was meeting some guy, I don’t even remember who. After that, we took turns watching the corridor at night.’ Grim project-manager voice on Joanne; I could picture her going for the jugular if one of the others had the nerve to doze off at her post. ‘This night, Alison saw Selena sneak out of their room, so she woke me up and I followed Selena.’

‘You brought Gemma along?’

‘Um, I wasn’t exactly about to go out there by myself? And anyway, I needed Gemma to show me where they were having their little makeout sessions. By the time we got dressed, Selena was well gone. She couldn’t wait to get the action started. Some people are just sluts.’

More midnight traffic than a train station, these grounds. McKenna was in for a coronary if she ever heard this. ‘So you tracked them down,’ I said, ‘and you filmed this clip. Just the one?’

‘Yeah. That’s not enough for you?’

‘What happened after you stopped filming?’

Joanne prissed up her mouth. ‘We went back in. I wasn’t going to stand there and watch them do it. I’m not a perv.’

Conway’s phone buzzed. ‘Sent myself the video,’ she told me. To Joanne: ‘Here.’ She tossed the mobile over.

Joanne made a big deal of wiping off the working-class germs on her duvet. I asked, ‘What were you planning to do with this clip?’

Shrug. ‘I hadn’t decided yet.’

Conway said, ‘Wild guess. You used it to blackmail Selena into dumping Chris. “Stay away from him, or this goes to McKenna.”’

Joanne’s top lip pulled up, that near-animal snarl. ‘Um, excuse me, no I didn’t?’

I said – leaning forward, move her off Conway – ‘It would’ve been for Selena’s own good if you had. That there, that wasn’t the healthiest way for her to be spending her nights.’

Joanne thought that over, decided she liked it. Did something with her face that was meant to look virtuous, came out looking stuffed. ‘Well. I would’ve if I’d had to. But I didn’t.’

‘Why not?’

‘That’ – Joanne flicked a finger at the phone – ‘that was the last time Selena and Chris met up. I’d already had a chat with Julia, and after this she sorted it out. End of.’

‘How did you know?’