Conway started pacing again, but steady this time, none of that restless looking for something to wreck. She was focusing. ‘Why, but? She has to know the phone’s evidence. Hanging onto it is dangerous. Why not bin it, a year ago?’

‘Dunno. But it mightn’t be the actual phone she kept. She might’ve ditched the phone, just hung onto the SIM card. That’s a lot safer. Then today, she needs an anonymous number to text us from, swaps Chris’s SIM into her own phone . . .’

‘Why hang on to any of it?’

I said, ‘Say it’s Theory Two, the killer passed it on to someone else. Maybe the other girl had a feeling there was something dodgy about it, something to do with Chris; she hung onto the phone, or just the SIM card, in case she ever felt like turning it in to us. Or maybe she didn’t cop there was a connection, just liked the idea of having an anonymous number stashed away. Or maybe it just had credit left on it, like the one Joanne sold Alison.’

Conway nodded. ‘OK. That’ll work with Theory Two. I don’t see how it works with One or Three. Which means the girl who texted you isn’t the killer.’

I said, ‘That says the killer’s got plenty of nerve. Handing Chris’s phone off to someone else, instead of binning it, when it could put her in jail.’

‘Plenty of nerve, plenty of arrogance, plenty of stupid, take your pick. Or she didn’t hand it off on purpose; she ditched it somewhere, the texter found it.’

Voices, seeping down the corridor with the chicken-and-mushroom smell: the fourth-years talking over their dinner. Not happy girly chitchat. This was a low, flattened-out buzz, got into your ear and turned you edgy.

I said, ‘Did Sophie say when we’ll get the records off it?’

‘Soon. Her contact’s working on it. I’ll e-mail her now, tell her we need the actual texts, not just the numbers. We could be out of luck – some of the networks dump that stuff after a year – but we’ll give it a shot.’ Conway was typing fast. ‘Meanwhile,’ she said.

It was gone five o’clock. Meanwhile we go back to HQ, sort our paperwork, sign out. Meanwhile we get something to eat, get some kip, nice work today Detective Moran see you bright and early in the morning.

No way we could leave Kilda’s, not now. Inside, all those girls, all jittering to start swapping stories and matching up lies the second our shadow lifted. Outside, the Murder lads, jaws ready to snap shut on this case the minute O’Kelly heard it was live again. In the middle, us.

If we walked out of Kilda’s empty-handed, we’d never come back or we’d come back to a blank wall.

But: