He sighed, a tired little sound. "And after that…it was actually easier, you know? At least I didn't have to pretend everything was fine."

No wonder he had been spacey during that first interview. Not spacey enough to ring our alarm bells, though. For a novice, he had done pretty well. "And when we talked to you," I said, and then I stopped.

Cassie and I didn't look at each other, didn't move a muscle, but the realization shot between us like a jolt from an electric fence. One reason we had taken Jessica's Tracksuit Shadow story quite so seriously was that Damien had put the very same guy practically at the scene of the crime.

"When we talked to you," I said, after only a fractional pause, "you invented a big guy in a tracksuit, to throw us off."

"Yeah." Damien looked anxiously from one of us to the other. "Sorry about that. I just thought…"

"Interview suspended," Cassie said, and left. I followed her, with a sinking sensation in my stomach and Damien's faint apprehensive "Wait-what…?" drifting after us.

By some shared instinct, we didn't stay in the corridor or go back to the incident room. We went next door, into the interview room where Sam had been questioning Mark. There was still debris strewn on the table: crumpled napkins, Styrofoam cups, a splatter of dark liquid where someone had banged down a fist or shoved back a chair.

"All right!" Cassie said, on something between a gasp and a laugh. "We did it, Rob!" She tossed her notebook onto the table and threw an arm around my shoulders. The gesture was quick and glad and unthinking, but it set my teeth on edge. We had been working together with all the old perfect understanding, slagging each other as if nothing had ever been wrong, but this had been purely for Damien's benefit and because the case demanded it; and I did not think I should be required to explain this to Cassie.

"Apparently, yeah," I said.

"When he finally said it…God, I think my jaw practically hit the floor. Champagne tonight, whenever we're finished, and lots of it." She let out a deep breath, leaned back against the table and ran her hands through her hair. "You should probably go get Rosalind."

I felt my shoulders tighten. "Why?" I asked coolly.

"She doesn't like me."

"Yes, I'm aware of that. Why should anyone go get her?"

Cassie stopped in midstretch and stared at me. "Rob, she and Damien gave us the same exact fake lead. There has to be some connection there."

"Actually," I said, "Jessica and Damien gave us the same fake lead."

"You think Damien and Jessica are in on this together? Come on."

"I don't think anyone's in on anything. What I do think is that Rosalind has been through just about enough for one lifetime, and that there's not a chance in hell that she was an accomplice to her sister's murder, so I don't see the point of dragging her in here and putting her through even more trauma."

Cassie sat back on the table and looked at me. There was an expression in her eyes that I couldn't fathom. "Do you think," she inquired eventually, "that that little sap came up with this all by himself?"

"I don't know and I don't care," I said, hearing echoes of O'Kelly in my voice but unable to stop myself. "Maybe Andrews or one of his buddies hired him. That would explain why he's dodging the whole motive thing: he's scared they'll go after him if he rats them out."

"Yeah, except we don't have one single connection between him and Andrews-"

"Yet."

"-and we do have one between him and Rosalind."

"Did you hear me? I said, yet. O'Kelly's on the financials and the phone records. When they come back, we'll see what we're dealing with and take it from there."

"By the time the records come back, Damien'll have calmed down and got himself a lawyer, and Rosalind will have seen the arrest on the news and she'll be on her guard. We pull her in right now and we play them off each other till we find out what's going on."

I thought of Kiernan's voice, or McCabe's; of the vertiginous sensation as the ligaments of my mind gave way and I floated off into that soft, infinitely welcoming blue sky. "No," I said, "we don't. That girl is fragile, Maddox. She is sensitive and she is highly strung and she just lost a sister and she has no idea why. And your answer is to play her off her sister's killer? Jesus, Cassie. We have a responsibility to look after that girl."

"No we don't, Rob," Cassie said sharply. "No we don't. That's Victim Support's job. We have a responsibility to Katy, and a responsibility to try and find out the truth about what the hell happened here, and that's it. Anything else comes second."

"And if Rosalind goes into a depression or has a nervous breakdown because we've been harassing her? Are you going to claim that's Victim Support's problem, too? We could damage her for life here, do you understand that? Until we have something a whole lot better than a minor coincidence, we leave that girl the hell alone."

"Minor coincidence?" Cassie shoved her hands into her pockets, hard. "Rob. If this were anyone but Rosalind Devlin, what would you be doing right now?"

I felt a wave of anger rising inside me, sheer fury with a thick, tangled quality to it. "No, Maddox. No. Don't even try to pull that. If anything, it's the other way around. You've never liked Rosalind, have you? You've been dying for a reason to go after her since day one, and now that Damien's given you this pathetic shred of an excuse, you're diving on it like a starving dog on a bone. My God, that poor girl told me a lot of women were jealous of her, but I have to say I gave you more credit than that. Apparently I was wrong."

"Jealous of-Jesus Christ, Rob, you've got some nerve! I gave you more credit than to think you'd back off a fucking suspect just because you're sorry for her, and you fancy her, and you're pissed off with me for some bloody bizarre reason of your own-"

She was losing her temper fast, and I saw this with a hard pleasure. My anger is cold, controlled, articulate; it can smash a short-fuse explosion like Cassie's to pieces any day. "I wish you'd keep your voice down," I said. "You're embarrassing yourself."

"Oh, you think? You're an embarrassment to this entire fucking squad." She jammed her notebook into her pocket, pages crumpling. "I'm going to get Rosalind Devlin-"

"No you're not. For Christ's sake, act like a bloody detective, not like some hysterical teenager with a vendetta."

"Yeah, I am, Rob. And you and Damien can do whatever you like, you can crawl up each other's arse and die for all I care-"

"Well," I said, "that certainly puts me in my place. Very professional."

"What the fuck goes on in your head?" Cassie yelled. She kicked the door shut behind her with a bang, and I heard the echoes reverberate, deep and ominous, up and down the corridor.

I gave her plenty of time to leave. Then I went out for a cigarette-Damien could look after himself, like a big boy, for a few more minutes. It was starting to get dark and it was still raining, thick apocalyptic sheets. I turned up the collar of my jacket and squashed uncomfortably into the doorway. My hands were shaking. Cassie and I had had fights before, of course we had; partners argue as ferociously as lovers. Once I got her so furious that she slammed her hand down on her desk and her wrist swelled up, and we didn't speak for almost two days. But even that had been different; utterly different.

I threw away my soggy cigarette half-smoked and went back inside. Part of me wanted to send Damien off for processing and go home and let Cassie deal with that when she came back to find us gone, but I knew I didn't have that luxury: I needed to find out his motive, and I needed to do it in time to prevent Cassie from giving Rosalind the third degree.