"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?"