"Right," I said. "Your mystery man." It sounded plausible enough, but then Frank always does. I was still pretty sure that Sam was right and his main reason for doing this wasn't because he thought it had a snowball's chance in hell but because it was such a dazzling, reckless, ridiculous once-off. I decided I didn't care.

"Exactly. To go with our mystery girl. Meanwhile, keep an eye on the housemates and keep them talking. I don't rate them as suspects--I know your Sammy has a bee in his bonnet about them, but I'm with you, they don't add up--but I'm pretty sure there's something they're not telling us. You'll see what I mean when you meet them. It might be something completely irrelevant, maybe they just cheat on their exams or make moonshine in the back garden or know who's the daddy, but I'd like to decide for myself what's relevant here and what's not. They're never going to talk to cops, but if you go at it right, there's a good chance they'll talk to you. Don't worry too much about her other KAs--we've got nothing that points to any of them, and Sammy and I will be on them anyway--but if anyone's acting even slightly dodgy, obviously, report back to me. Got it?"

"Got it," I said.

"One last thing," said Frank. He unfolded himself from the table, found our coffee mugs and took them over to the kitchen. We had got to the point where there was always, every hour of the day or night, a large pot of strong coffee keeping warm on the cooker; another week and we would probably have been eating the grounds straight from the bag with a spoon. "I've been meaning to have a little chat with you for a while now."

I had felt this one coming for days. I flipped through the photos like flash cards and tried to concentrate on running the names in my head: Cillian Wall, Chloe Nelligan, Martina Lawlor . . . "Hit me," I said.

Frank put the mugs down and started playing with my saltcellar, turning it carefully between his fingers. "I hate to bring this up," he said, "but what can you do, sometimes life sucks. You're aware that you've been--how shall I put this--a little jumpy lately, yeah?"

"Yeah," I said, keeping my eyes on the photos. Isabella Smythe, Brian Ryan--someone's parents either hadn't been thinking too clearly, or had a weird sense of humor--Mark O'Leary ... "I'm aware."

"I don't know if it's because of this case or if it was going on already or what, and I don't need to know. If it's just stage fright, it might well vanish as soon as you're inside that door. But here's what I wanted to say to you: if it doesn't, don't panic. Don't start second-guessing yourself, or you'll talk yourself into losing your nerve, and don't try to hide it. Use it. There's no reason why Lexie shouldn't be a little shaky right now, and there's no reason why you shouldn't make that work for you. Use what you've got, even if it's not necessarily what you'd have chosen. Everything's a weapon, Cass. Everything."