The thought of twelve-year-olds kissing startled me, but I remembered Katy's friends, those knowing, disconcerting little girls. Maybe Peter and Jamie and I had just been backwards. "Are you positive? Your father seemed pretty sure."

"My father…" There was a tiny frown-line between Rosalind's eyebrows. "My father worshipped Katy. And she…sometimes she took advantage of that. She didn't always tell him the truth. That made me very sad."

"OK," I said. "OK. I understand. You've done the right thing by telling me." She nodded, just a slight inclination of the head. "I need to ask you one more thing. You ran away from home in May, right?"

The frown deepened. "I didn't exactly run away, Detective Ryan. I'm not a child. I spent a weekend with a friend."

"Who was that?"

"Karen Daly. You can ask her, if you'd like. I'll give you her number."

"There's no need," I said, ambiguously. We had already talked to Karen-a timid, pasty-faced girl, not at all what I would have expected a friend of Rosalind's to be-and she had confirmed that Rosalind had been with her all weekend; but I have a fairly good nose for deception, and I was pretty sure there was something Karen wasn't telling me. "Your cousin thought you might have spent the weekend with a boyfriend."

Rosalind's mouth tightened into a displeased little line. "Valerie has a dirty mind. I know a lot of other girls do things like that, but I'm not other girls."

"No," I said. "You're not. But your parents didn't know where you were?"

"No. They didn't."

"Why was that?"

"Because I didn't feel like telling them," she said sharply. Then she glanced up at me and sighed, and her face softened. "Oh, Detective, don't you ever feel that-that you just need to get away? From everything? That it's all just too much?"

"I do," I said, "yes. So the weekend away wasn't because anything bad had happened at home? We've been told you had a fight with your father…"

Rosalind's face clouded over, and she looked away. I waited. After a moment, she shook her head. "No. I…nothing like that."

My alarm bells were going off again, but her voice had tightened and I didn't want to push her, not yet. I wonder now, of course, whether I should have; but I can't see that, in the long run, it would have made any difference to anything at all.

"I know you're having a very hard time right now," I said, "but don't run away again, OK? If things are getting on top of you, or if you just want to talk, give Victim Support a ring, or call me-you have my mobile number, right? I'll do whatever I can to help."

Rosalind nodded. "Thank you, Detective Ryan. I'll remember that." But her face was withdrawn, subdued, and I had the sense that, in some obscure but critical way, I had let her down.

Cassie was in the squad room, photocopying statements. "Who was that?"

"Rosalind Devlin."

"Huh," Cassie said. "What did she say?"

For some reason, I didn't feel like telling her the details. "Nothing much. Just that, no matter what Jonathan thought, Katy was into boys. Rosalind didn't know any names; we'll need to talk to Katy's mates again and see if they can give us more. She also said Katy told lies, but then, most kids do."

"Anything else?"

"Not really."

Cassie turned from the photocopier, a page in her hand, and gave me a long look I couldn't read. Then she said, "At least she's talking to you. You should stay in touch with her; she might open up more as you go."

"I did ask her whether there was anything wrong at home," I said, a little guiltily. "She said no, but I didn't believe her."

"Hmm," Cassie said, and went back to photocopying.

But when we talked to Christina and Marianne and Beth again, the next day, they were all adamant: Katy had had no boyfriends and no particular crushes. "We used to tease her about guys sometimes," Beth said, "but not really, you know? Just messing." She was a redheaded, cheerful-looking kid, already sprouting boisterous curves, and when her eyes filled with tears she seemed bewildered by them, as if crying was still an unfamiliar thing. She fished in the sleeve of her sweater and pulled out a tattered tissue.

"She might not have told us, though," said Marianne. She was the quietest of the bunch, a pale fairy of a girl vanishing into her funky teenage clothes. "Katy's-Katy was very private about stuff. Like the first time she auditioned for ballet school, we didn't even know about it till she got accepted, remember?"

"Um, hel-lo, not the same thing," Christina said, but she had been crying, too and the stuffed nose took most of the authority off her voice. "We couldn't exactly have missed a boyfriend."

The floaters would re-interview every boy on the estate and in Katy's class, of course, just in case; but I realized that, at some level, this was exactly what I had been expecting. This case was like an endless, infuriating streetcorner shell game: I knew the prize was in there somewhere, right under my eye, but the game was rigged and the dealer much too fast for me, and every sure-thing shell I turned over came up empty.

Sophie rang me as we were leaving Knocknaree, to say that the lab results were back. She was walking somewhere; I could hear the mobile jolting and the fast, decisive taps of her shoes.

"I've got your results on the Devlin kid," she said. "The lab's got a six-week backlog, and you know what they're like, but I got them to jump this one up the queue. I practically had to sleep with the head geek before he'd do it."

My heart rate picked up. "Bless you, Sophie," I said. "We owe you another one." Cassie, driving, glanced across at me; I mouthed, "Results."

"Tox screen was negative: she wasn't drugged, drunk or on any medication. She was covered in trace, mostly outdoor stuff-dirt, pollen, the usual. It's all consistent with the soil composition around Knocknaree, even-this is the good part-even the stuff that was inside her clothes and stuck to the blood. So stuff she didn't just pick up at the dump site. Lab says there's some super-rare plant in that wood that doesn't grow anywhere else nearby-it got the plant geek very turned on, apparently-and the pollen wouldn't blow more than a mile or so. The odds are she was in Knocknaree the whole time."

"That fits with what we have," I said. "Get to the good stuff."

Sophie snorted. "That was the good stuff. The footprints are a dead end: half of them match the archaeologists, and the ones that don't are too blurry to be any use. Practically all the fibers are consistent with stuff we pulled from the home; a handful of unidentified ones, but nothing distinctive. One hair on the T-shirt matching the idiot who found her, two that match the mother-one on the combats, one on a sock, and she probably does the washing, so no big deal there."

"Any DNA? Or fingerprints or anything?"

"Ha," Sophie said. She was eating something crunchy, probably crisps-Sophie lives mainly on junk food. "A few bloody partials, but they came off a rubber glove-surprise, surprise. So no epithelials, either. And no semen and no saliva, and no blood that doesn't match the kid."

"Great," I said, my heart slowly sinking. I had fallen for the con all over again, I had got my hopes up, and I felt suckered and stupid.

"Except for that old spot Helen found. They got a blood type off it: it's A positive. Your victim's O neg."

She paused for another mouthful of crisps, while my stomach did something complicated. "What?" she demanded, when I said nothing. "That's what you wanted to hear, isn't it? Same as the blood from the old case. OK, so it's tentative, but at least it's a link."