“Here’s what your scenarios have in common,” Frank said. He was lying back with his arms folded behind his head, watching us, and that glint in his eye had got cockier. “Our guy planned to meet her once, which means he might very well want to meet her again, given the chance. He didn’t plan to kill her, which means it’s highly unlikely that there’s any further danger. And he came from outside Whitethorn House.”

“Not necessarily,” Sam said. “If one of the housemates did it, he-or she-might have taken Lexie’s mobile off her body, to make sure she hadn’t called 999 or recorded anything. We know she used the video camera all the time; they could well have been worried that she’d put the attacker’s name on there.”

“Prints from the phone back yet?” I asked.

“This afternoon,” Frank said. “Lexie and Abby. Both Abby and Daniel say that Abby passed Lexie her mobile that morning, on their way out to college, and the prints back that up. Lexie’s are overlaid on Abby’s in at least two places: she touched the phone after Abby did. Nobody took that phone off Lexie’s body. It was at home on the kitchen table when she died, and any of the housemates could have found that out without needing to chase after her.”

“Or they could’ve taken her diary,” said Sam. “We’ve only their word for it that she didn’t keep one.”

Frank rolled his eyes. “If you want to play that game, we’ve only got their word for it that she even lived there. For all we know, she could have had a row with them a month ago and moved into the penthouse of the Shelbourne as the mistress of a Saudi prince, except there’s not one speck of evidence that points that way. All four of their stories match up perfectly, we haven’t caught any of them in a lie, she got stabbed outside the house-”

“What do you think?” Sam asked me, cutting Frank off. “Do they fit the profile?”

“Yeah, Cassie,” Frank said sweetly. “What do you think?”

Sam so badly wanted it to be one of them. For a moment I actually wished I could say it was, and never mind what that would do to the investigation, just to see the drained look evaporate off his face, a spark come into his eyes. “Statistically,” I said, “sure, close enough. They’re the right age, they’re local, they’re smart, they knew her-not just that: they’re the ones who knew her best, and that’s where you mostly find your killer. None of them has a record, but like I said, one of them could have done stuff we don’t know about, somewhere along the way. At first, yeah, I liked them for it. The more I hear, though…” I ran my hands through my hair and tried to figure out how to say this. “Here’s the one thing I don’t like taking their word for. Do we have any kind of independent confirmation that she normally went for these walks on her own? That none of the housemates went with her?”

“Actually,” Frank said, feeling on the floor for his smokes, “we do. There’s an English postgrad called Brenda Grealey, had the same supervisor as Lexie.” Brenda Grealey was on the KA list: large, with sticking-out gooseberry eyes, plump cheeks already beginning to droop and a lot of ginger curls. “She’s the nosy type. After the five of them moved in together, she asked Lexie if she ever got any privacy, living with all those guys. I get the feeling Brenda meant it as a double entendre, she was hoping for some kind of wild sex gossip, but apparently Lexie just gave her a blank look and said she went for solo walks every evening and that was all the privacy she needed, thanks, she didn’t hang out with people unless she liked their company. Then she walked off. I’m not sure our Brenda realized she’d been bitchslapped.”

“OK,” I said. “In that case, I really can’t see a way to make any of the housemates work. Look at how it would’ve had to play out. One of them needs to talk to Lexie in private, about something big. So, instead of going about it the inconspicuous way, bringing her for coffee in college or whatever, he goes on her walk with her, or follows her out. Either way, he’s breaking the routine-and those five are all about the routine-and telling everyone including Lexie, loud and clear, that something’s up. And then he brings along a knife. These are nice middle-class intellectuals we’ve got here-”

“She means they’re a bunch of nancy boys,” Frank informed Sam, over the click of his lighter.

“Ah, here,” Sam said, putting his pen down. “Hang on. You can’t rule them out just because they’re middle-class. How many cases have we worked where some lovely, respectable-”

“I’m not, Sam,” I said. “The killing’s not the problem. If she’d been choked to death, or had her head smashed off a wall, I’d be fine with one of them as the doer. I don’t even have a problem with the idea of one of them stabbing her, if he happened to be there with the knife in his hand. What I’m saying is that he wouldn’t have the knife on him to begin with-not unless he was actually planning to kill her, and like I said before, that doesn’t fit. I’m willing to bet serious money that those four don’t make a habit of carrying knives around; and if they just wanted to threaten someone, or convince someone, it wouldn’t even occur to them to use a knife to do it. That’s not the world they live in. When they gear up for a big fight, they prepare by thinking out debate points, not picking out knives.”

“Yeah,” Sam said, after a moment. He took a deep breath and picked up his pen again, left it hanging above the page as if he’d forgotten what he meant to write. “I suppose they do, sure.”

“Even if we go with the idea that one of them followed her,” I said, “and brought along a knife to scare her with for some reason, what did he think was going to happen next? Did he seriously expect to get away with it? They’re part of the same social circle. It’s tiny, and it’s intimate. There’s no reason why she shouldn’t agree to anything he wanted, then head straight home and tell the other three exactly what had happened. Cue shock, horror, and quite possibly-unless it’s Daniel-our knife-wielder getting thrown out of Whitethorn House. These are smart people, Sam. They couldn’t overlook something that obvious.”

“In fairness,” Frank said helpfully, switching sides-apparently he was getting bored-“smart people do stupid things all the time.”

“Not like that,” Sam said. He left his pen lying across his notebook and pressed two fingers into the corners of his eyes. “Stupid things, yeah, sure. Not things that make no sense at all.”

I had put that look on his face, and I felt like crap. “Do they do drugs?” I asked. “People on coke, say, don’t always think straight.”

Frank snorted smoke. “I doubt it,” said Sam, without looking up. “They’re straight arrows, this lot. They take a drink, all right, but from the looks of them I wouldn’t say they’d even be into the odd bit of hash, never mind the hard stuff. Our girl’s tox screen came back clean as a whistle, remember?”

The wind hurled itself up against the window with a bang and a rattle, fell away again. “Then, unless we’re missing something huge,” I said, “they just don’t add up.”

After a moment Sam said, “Yeah.” He closed his notebook carefully, clipped the pen onto it. “I’d better start looking for something huge, then.”

“Can I ask you a question?” Frank inquired. “Why do you have such a hard-on for these four?”

Sam rubbed his hands down his face and blinked hard, like he was trying to focus. “Because they’re there,” he said, after a moment. “And no one else is, at least not so’s you’d notice. Because if it’s not them, what’ve we got?”

“You’ve got that lovely profile,” Frank reminded him.

“I know,” Sam said, heavily. “And I appreciate it, Cassie; I do, honest. But right now I’ve got no one that matches it. I’ve plenty of local fellas-women as well-in the right age group, some of them have records and I’d say there’s a good few are smart and organized, but there’s no sign that any of them ever met our girl. I’ve plenty of acquaintances from college, and a few of them tick just about all the boxes, except as far as I can find out they’ve never so much as been to Glenskehy, never mind knowing their way around the place. There’s no one who matches right across the board.”