“And lots of it. We’ve got work to do. Gonna be another long night, babe.”

“Surprise, surprise,” I said. “What’s Olivia think of you sleeping over at my place?”

I was fishing, and I knew from the fraction of a pause as Frank pushed his plate away that I had guessed right: undercover strikes again. “Sorry,” I said. “I didn’t mean to-”

“Yeah, you did. Olivia got smart and dumped me last year. I get Holly one weekend a month and two weeks in summer. What’s your Sammy think of me sleeping over at your place?”

His eyes were cool and unblinking and he didn’t sound annoyed, just firm, but the message was clear: Back off. “He’s fine with it,” I said, getting up to check the coffee. “Anything for the job.”

“You think? The job didn’t seem to be his main priority on Sunday.”

I changed my mind: he was pissed off with me about the Olivia thing. Apologizing would only make it worse. Before I could think of anything useful to say, my buzzer rang. I managed to keep the jump down to a minimum, had a graceful Inspector Clouseau moment where I whacked myself neatly across the shin with the sofa corner on my way to the door, and caught Frank’s sharp, curious up-glance.

It was Sam. “And there’s your answer,” Frank said, grinning and hoisting himself up off the floor. “You, he’d trust anywhere, but me he’s keeping an eye on. I’ll take care of the coffee; you go canoodle.”

Sam was exhausted; I could feel it in the weight of his body when he kissed me, the way he let out his breath in something like a sigh of relief. “God, it’s good to see you,” he said; then, as he spotted Frank waving from the kitchen, “Oh.”

“Welcome to the Lexie Lab,” Frank said cheerfully. “Coffee? Sweet and sour pork? Prawn cracker?”

“Yeah,” Sam said, blinking. “I mean, no; just coffee, thanks. I won’t stay, if you’re working; I just wanted to… Are you busy?”

“You’re fine,” I told him. “We were having dinner. What’ve you eaten today?”

“I’m grand,” Sam said vaguely, dumping his holdall on the floor and struggling out of his coat. “Could I borrow you for a few minutes? If you’re not in the middle of something.”

He was asking me, but Frank said expansively, “Why not? Have a seat, have a seat,” and waved him to the futon. “Milk? Sugar?”

“No milk, two sugars,” Sam said, collapsing onto the futon. “Thanks.” I was pretty sure that he was starving, that he wasn’t going to touch anything Frank had bought, that the holdall contained all the ingredients for something a lot more evolved than lemon chicken, and that if I could just get my hands on his shoulders I could rub that tension away in five minutes flat. Going undercover was starting to seem like the easy part here.

I sat next to Sam, as close as I could get without touching. “How’s it going?” I asked.

He gave my hand a quick squeeze and reached round to his coat, draped over the back of the futon, to find his notebook. “Ah, sure, all right, I suppose. Just eliminating, mostly. Richard Doyle, your man who found the body, his alibi’s solid. We’ve ruled out all the DV files you flagged; we’re working on the rest and on your murder cases, but nothing yet.” The thought of the Murder squad combing through my files, with the rumors sizzling in their heads and my face for victim, sent a nasty little twitch down between my shoulder blades. “It doesn’t look like she used the internet at all-no internet activity under her log-in on the college computers, no MySpace page or anything like that, the e-mail address Trinity assigned her hasn’t even been used-so no leads there. And not even a sniff of any arguments in college-and the English department is mad for the old rumors. If she’d had problems with anyone, we’d have heard.”

“I hate to say I told you so,” Frank said sweetly, gathering up mugs, “but sometimes, in life, we have to do things we hate.”

“Yeah,” Sam said absently. Frank bent to hand him his coffee with a servile little flourish, and winked at me behind Sam’s back. I ignored him. One of Sam’s rules is that he doesn’t fight with anyone working the same case, but there are always people like Frank who figure he’s just too thick to notice when he’s being messed with. “So I wondered, Cassie… The thing is, eliminating could take forever, but as long as I’ve no motive and no leads, I’ve no other choice; there’s nothing to tell me where to start. I thought, if I just had some idea what I was looking for… Could you profile this for me?”

For a second I felt like the air in the room had gone dark with pure sadness, bitter and ineradicable as smoke. Every murder case I ever pulled, I had done my best to profile right here in my flat: late nights, whiskey, Rob stretched out on the sofa cat’s-cradling an elastic band and testing everything I came up with for holes. On Operation Vestal we’d brought Sam along, Sam smiling shyly at me while music and moths swirled at the windowpane, and all I could think was how happy the three of us had been, in spite of everything, and how fatally, devastatingly innocent. This prickly, crowded place-greasy smell of cold Chinese, my shin hurting like hell, Frank watching with those sidelong amused eyes-this wasn’t the same thing, it was like a mocking reflection in some creepy distorting mirror, and all I could think was, ludicrously, I want to go home.

Sam moved a sheaf of maps to one side-gingerly, glancing up at us to make sure he wasn’t messing anything up-and put down his mug. Frank scooted his arse to the very edge of the sofa, leaned his chin on his interlaced fingers and did enthralled. I kept my eyes down so they wouldn’t see the look on my face. There was a photo of Lexie on the table, half hidden under a carton of rice; Lexie up a ladder in the kitchen of Whitethorn House, wearing dungarees and a man’s shirt and an awful lot of white paint. For the first time ever, the sight of her felt good: that handcuff bite on my wrist jerking me down to earth, that cold-water slap in the face slamming everything else out of my mind. I almost reached out and pressed my hand onto the picture.

“Yeah, sure, I’ll profile,” I said. “You know I can’t give you a lot, though, right? Not on one crime.” Most of profiling is built on patterns. With a stand-alone crime, you have no way of knowing what’s pure chance and what’s a clue, stenciled in by the boundaries of your guy’s life or by the secret jagged outlines of his mind. One murder on a Wednesday evening tells you nothing very much; three more matching ones say that your guy has a window that night, and you might want to look twice when you find a suspect whose wife plays Bingo on Wednesdays. A phrase used in one rape could mean nothing; used in four, it becomes a signature that some girlfriend or wife or ex, somewhere, is going to recognize.

“Anything,” Sam said. He flipped his notebook open, pulled out his pen and leaned forwards, eyes fixed on me, ready. “Anything at all.”

“OK,” I said. I didn’t even need the file. I had spent more than enough time thinking about this, while Frank snored like a water buffalo on the sofa and my window went from black to gray to gold. “The first thing is that it’s probably a man. We can’t rule out a woman for definite-if you get a good female suspect, don’t ignore her-but statistically, stabbing’s usually a male crime. For now, we’ll go with a guy.”

Sam nodded. “That’s what I figured, too. Any ideas on what age he is?”

“This isn’t a teenager; he’s too organized and too controlled. We’re not talking about an old man, either, though. This didn’t take an athlete, but it did take a basic level of fitness-running around lanes, climbing over walls, dragging a body. I’d go with twenty-five to forty, give or take.”

“And I’m thinking,” Sam said, scribbling, “there’s local knowledge there.”

“Oh yeah,” I said. “Either he’s local or he’s spent an awful lot of time around Glenskehy, one way or another. He’s very comfortable in the area. He hung around for ages after the stabbing; killers who’re off their turf tend to get uneasy and split as fast as they can. And going by the maps, the place is a maze, but he managed to find her-in the dead of night, with no street lamps-after she got away from him.”