"Good," said Cassie, diving into the wardrobe again and coming up with a glass tumbler that said NUTELLA on the side. "I hate when some people are drinking and some aren't. It makes the conversation go all lopsided. What the hell did you do to Cooper, by the way?"

Sam laughed, relaxed and rummaged for the corkscrew. "I swear, that wasn't my fault. My first three cases all came in at five in the evening; I rang him just when he was getting home."

"Uh-oh," Cassie said. "Bad Sam."

"You're lucky he'll talk to you," I said.

"Barely," said Sam. "He still pretends he can't remember my name. He calls me Detective Neary or Detective O'Nolan-even on the stand. Once he called me a different name every time he mentioned me, and the judge got so confused he almost declared a mistrial. Thank God he likes the pair of ye."

"It's Ryan's cleavage that does it," said Cassie, nudging me out of the way with her hip and throwing a handful of salt into the pan of water.

"I'll buy a Wonderbra," Sam said. He uncorked the bottle deftly, poured the wine and put glasses into our free hands. "Cheers, lads. Thanks for inviting me over. Here's to a quick solve and no nasty surprises."

After dinner we got down to business. I made coffee; Sam insisted on washing up. Cassie had the post-mortem notes and photos spread out on her coffee table, an old wooden chest beeswaxed to a shine, and she was sitting on the floor flipping back and forth, eating cherries from the fruit bowl with her other hand. I love watching Cassie when she's concentrating. Utterly focused, she is as absent and unselfconscious as a child-twisting a finger in a curl at the back of her head, pulling her legs into effortlessly odd angles, flipping a pen around her mouth and abruptly pulling it out to murmur something to herself.

"While we're waiting for Miss Cleo over there," I said to Sam-Cassie gave me the finger without looking up-"how was your day?"

Sam was rinsing plates with neat, bachelor efficiency. "Long. Hold music, and all these civil servants telling me I needed to speak to someone else and then putting me through to voicemail. It's not going to be as easy as it sounds, finding out who owns that land. I did talk to my uncle, asked him if this Move the Motorway was actually having any effect."

"And?" I said, trying not to sound cynical. I had nothing against Redmond O'Neill in particular-I had a vague image of a big, ruddy man with a shock of silver hair, but that was all-but I do have a firm general mistrust of politicians.

"He said no. Basically, he says, they're just a nuisance-" Cassie glanced up, raised an eyebrow. "I'm only quoting. They've been to court a few times, trying to stop the motorway; I've still to check the exact dates, but Red says the hearings were at the end of April, the beginning of June and the middle of July. That matches the phone calls to Jonathan Devlin."

"Apparently someone thought they were more than just a nuisance," I said.

"This last time in court, a few weeks ago, Move the Motorway got an injunction, but Red says it'll be thrown out on appeal. He's not worried."

"Well, that's nice to know," Cassie said sweetly.

"That motorway will do a lot of good, Cassie," Sam said gently. "There'll be new houses, new jobs-"

"I'm sure it will. I just don't see why it couldn't do all that good a few hundred yards to one side."

Sam shook his head. "I wouldn't know, sure. I don't understand all that stuff. But Red does, and he says it's badly needed."

Cassie was opening her mouth to say something else, but I caught the glint in her eye. "Stop being a brat and profile," I told her.

"OK," she said, as we brought over the coffee, "the main interesting thing is that it looks to me like this guy's heart wasn't in it."

"What?" I said. "Maddox, he smacked her twice over the head and then suffocated her. She was very, very dead. If he hadn't been serious about it-"

"No, hang on," Sam said. "I want to hear this." My job in the amateur profiling sessions is to play devil's advocate, and Cassie is well able to shut me up if I get overenthusiastic, but Sam has an ingrained, old-fashioned chivalry that I find admirable as well as slightly annoying. Cassie shot me a wicked sideways look and smiled at him.

"Thanks, Sam. As I was saying. Look at the first blow: it was only a tap, barely enough to knock her over, never mind knock her out. She had her back to him, she wasn't moving, he could have smashed her head in; but he didn't."

"He didn't know how much force it would take," Sam said. "He hadn't done this before." He sounded unhappy. This may seem callous, but we often prefer the signs to point to a serial offender. That way there might be other cases to cross-check with, more evidence to collate. If our guy was a first-timer, we had nothing to go on but this.

"Cass?" I said. "You think he's a virgin?" I realized, as I said it, that I had no idea what I wanted the answer to be.

She reached for the cherries absently, her eyes still on the notes, but I saw her eyelashes flicker: she knew what I was asking. "I'm not sure. He hasn't done this often, or recently, or he wouldn't have been this tentative about it. But he could have done it once or twice before, awhile ago. We can't rule out a link to the old case."

"It's unusual for a serial killer to take twenty years off," I said.

"Well," Cassie said, "he wasn't too crazy about doing it this time. She fights, he gets a hand over her mouth, he hits her again-maybe as she's trying to crawl away, something like that-and this one knocks her out. But, instead of keeping on hitting her with the rock-even though they've been struggling and his adrenaline must be through the roof at this stage-he drops it and suffocates her. He doesn't even strangle her, which would be a whole lot simpler: he uses a plastic bag, and from behind so he won't have to see her face. He's trying to distance himself from the crime, make it seem less violent. Gentler." Sam grimaced.

"Or he doesn't want to make a mess," I said.

"OK, but then why hit her at all? Why not just jump her and stick the bag over her head? I think he wanted her out cold because he didn't want to see her suffer."

"Maybe he wasn't confident that he'd be able to subdue her unless he knocked her out right away," I said. "Maybe he's not very strong-or, again, he's a first-timer and he doesn't know what it'll take."

"Fair enough. Maybe a little of all three. I agree that we're looking for someone with no known history of violence-someone who never even got into fights in the schoolyard, wouldn't be considered physically aggressive at all-and probably no history of sexual assault, either. I don't think the rape was really a sex crime."

"What, because he used an object?" I said. "You know some of them can't get it up." Sam blinked, startled, took a sip of coffee to cover it.

"Sure, but then he would've been more…thorough." We all winced. "From what Cooper said, it was a token gesture: one thrust, no sadism, no frenzy, only a couple of inches' worth of abrasion, barely tore the hymen. And it was post-mortem."

"That could be by choice. Necrophilia."

"Jesus," Sam said, putting the coffee down.

Cassie looked for her cigarettes, changed her mind and took one of my strong ones. Her face, momentarily off guard as she tilted it to the lighter flame, looked tired and quenched; I wondered if that night she would dream about Katy Devlin, pinned down and trying to scream. "He'd have kept her for longer. And, again, there'd be signs of more comprehensive sexual assault. No: he didn't want to do it. He did it because he had to."

"Staging a sex crime to put us on the wrong track?"

Cassie shook her head. "I don't know…If that was it, you'd expect him to make a point of it: strip her, pose her with her legs spread. Instead, he pulls her combats up again, zips them… No, I was thinking maybe something more along the lines of schizophrenia. They're almost never violent, but if you get one off his meds and in a full-on paranoid phase, you never know. He could have believed, for some reason of his own, that she had to be killed and raped, even though he hated doing it. That would explain why he tried not to hurt her, why he used an object, why it didn't look more like a sex crime-he didn't want her exposed, and he didn't want anyone thinking of him as a rapist-even why he left her on the altar."