Holly’s head moved, a blind flinch. ‘Anyone can confess to anything. She said it because she was scared you were going to arrest me.’

I said, ‘You already knew it was her.’

Holly didn’t deny it. She didn’t ask what would happen to Rebecca next; didn’t need to. She didn’t throw herself on the others, didn’t rush into Daddy’s arms – he managed not to go to her. She just stood there, watching her mates motionless on the grass, with one hand braced against a tree like it was holding her up.

‘If you’d known this morning,’ I said, ‘you’d never have brought me that card. Who did you think it was?’

Holly said, and she sounded way too tired and hollow for sixteen, ‘I always thought it was Joanne. Probably not actually her – I thought she made someone else do it, maybe Orla; she makes Orla do all her dirty work. But I thought it was her idea. Because Chris had dumped her.’

‘And then you figured Alison or Gemma found out, couldn’t take the pressure, put up the card.’

‘I guess. Yeah. Whatever. Gemma wouldn’t, but yeah, it’s exactly the kind of hello-are-you-actually-that-thick thing Alison would do.’

Conway asked, ‘Why didn’t you just say all this to Detective Moran, straight up? Why make us dick around jumping through hoops all day?’

Holly looked at Conway like just the thought of all that stupid made her want to sleep for a year. She let her back slump against the tree-trunk and closed her eyes.

I said, ‘You didn’t want to be a rat.’

Rustle behind her, sharp and then gone, as Mackey moved.

‘Again,’ Holly said. Her eyes stayed closed. ‘I didn’t want to be a rat again.’

‘If you’d told me everything you knew, you would’ve probably ended up testifying in court, and the rest of the school would’ve found out you’d squelt. But you still wanted the killer caught. That card was the perfect chance. You didn’t have to tell me anything; just point me in the right direction, and keep your fingers crossed.’

Holly said, ‘You weren’t stupid, last time. And you didn’t act like anyone under twenty had to be stupid. I thought if I could just get you in here . . .’

Conway said, ‘And you were right.’

‘Yeah,’ Holly said. The lines of her face, turned up to the sky, would have broken your heart. I couldn’t look at Mackey. ‘Go me.’

I asked, ‘How did you figure out it wasn’t Joanne after all? When we came to take you to the art room, you knew. What happened?’

Holly’s chest lifted and fell. ‘When that light bulb blew up,’ she said. ‘I knew then.’

‘Yeah? How?’

She didn’t answer. She was done.