"Got any evidence?" O'Kelly demanded, finally. "Or are you just going on Donnelly's word?"
"No hard evidence, no," Cassie said. "We can prove the connection between Damien and Rosalind-we've got calls between their mobiles-and they both gave us the same fake lead about some nonexistent guy in a tracksuit, which means she was an accessory after the fact, but there's no proof that she even knew about the murder beforehand."
"Of course there isn't," he said flatly. "Why did I ask. Are you all three on board with this? Or is this just Maddox's personal little crusade?"
"I'm with Detective Maddox, sir," Sam said firmly and promptly. "I've been interrogating Donnelly all day, and I think he's telling the truth."
O'Kelly sighed, exasperated, and jerked his chin at me. Obviously he felt Cassie and Sam were being gratuitously difficult, he just wanted to finish Damien's paperwork and declare this case closed; but in spite of his best efforts he is not a despot at heart, and he wouldn't override his team's unanimous opinion. I felt for him, really: I was presumably the last person he wanted to look to for support.
Finally-somehow I couldn't bear to say it out loud-I nodded. "Brilliant," O'Kelly said wearily. "That's just brilliant. All right. Donnelly's story's barely enough for us to charge her, never mind convict her. We need to get a confession. What age is she?"
"Eighteen," I said. I hadn't spoken in so long that my voice came out as a startled croak; I cleared my throat. "Eighteen."
"Thank Christ for small mercies. At least we don't have to have the parents there when we interrogate her. Right: O'Neill and Maddox, pull her in, go at her as hard as you can, scare the bejasus out of her till she cracks."
"Won't work," Cassie said, adding another branch to the tree. "Psychopaths have very low anxiety levels. You'd have to stick a gun to her head to scare her that badly."
"Psychopaths?" I said, after a startled instant.
"Jesus, Maddox," O'Kelly said, annoyed. "Less of the Hollywood. She didn't eat the sister."
Cassie glanced up from her doodle, her eyebrows lifting into cool, delicate arcs. "I wasn't talking about movie psychos. She fits the clinical definition. No conscience, no empathy, pathological liar, manipulative, charming, intuitive, attention-seeking, easily bored, narcissistic, turns very nasty when she's thwarted in any way…I'm sure I'm forgetting a few of the criteria, but does that sound about right?"
"That's enough to be going on with," Sam said dryly. "Hang on; so even if we go to trial, she'll get off on insanity?" O'Kelly mumbled something disgusted, no doubt to do with psychology in general and Cassie in particular.
"She's perfectly sane," Cassie said crisply. "Any psychiatrist will say so. It's not a mental illness."
"How long have you known this?" I asked.
Her eyes flicked to me. "I started wondering the first time we met her. It didn't seem relevant to the case: the killer clearly wasn't a psychopath, and she had a perfect alibi. I considered telling you anyway, but do you really think you would have believed me?"
You should have trusted me, I almost said. I saw Sam look back and forth between us, perplexed and unsettled.
"Anyway," Cassie said, going back to her sketching, "there's no point in trying to scare a confession out of her. Psychopaths don't really do fear; mainly just aggression, boredom or pleasure."
"OK," Sam said. "Fair enough. Then what about the other sister-Jessica, is it? Would she know anything?"
"Quite possibly," I said. "They're close." One corner of Cassie's mouth went up wryly at the word I had chosen.
"Ah, Jesus," O'Kelly said. "She's twelve, am I right? That means the parents."
"Actually," Cassie said, not looking up, "I doubt talking to Jessica would be any use either. She's completely under Rosalind's control. Whatever Rosalind's done to her, she's so punch-drunk that she can hardly think for herself. If we find a way to charge Rosalind, yeah, we might get something out of Jessica sooner or later; but as long as Rosalind's in that house, she'll be too terrified of saying something wrong to say anything at all."
O'Kelly lost patience. He hates being baffled, and the charged, crisscrossing tensions in the room must have been setting his teeth on edge just as badly as the case itself. "That's great, Maddox. Thanks for that. So what the hell do you suggest? Come on; let's hear you come up with something useful, instead of sitting there shooting down everyone else's ideas."
Cassie stopped drawing and carefully balanced her pen across one finger. "OK," she said. "Psychopaths get their kicks by having power over other people-manipulating them, inflicting pain. I think we should try playing to that. Give her all the power she can eat, and see if she gets carried away."
"What are you talking about?"
"Last night," Cassie said slowly, "Rosalind accused me of sleeping with Detective Ryan."
Sam's head turned sharply towards me. I kept my eyes on O'Kelly. "Oh, I hadn't forgotten, believe me," he said heavily. "And it bloody well better not be true. You two are both in deep enough shite already."
"No," Cassie said, a trifle wearily, "it's not true. She was just trying to distract me and hoping she would hit a nerve. She didn't, but she doesn't know that for sure; I could just have been covering very well."
"So?" O'Kelly demanded.
"So," Cassie said, "I could go talk to her, admit that Detective Ryan and I have a longstanding affair, and beg her not to turn us in-maybe tell her we suspect she was involved in Katy's death and offer to tell her how much we know in exchange for her silence, something like that."
O'Kelly snorted. "And what, you think she'll just spill her guts?"
She shrugged. "I don't see why not. Yeah, most people hate to admit they've done something terrible, even if they won't get in trouble for it; but that's because they feel bad about it, and because they don't want other people to think less of them. To this girl, other people aren't real, any more than characters in a video game, and right and wrong are just words. It's not like she feels any guilt or remorse or anything about having Damien kill Katy. In fact, I'm willing to bet she's over the moon with herself. This is her greatest achievement yet, and she hasn't been able to brag to anyone about it. If she's sure she has the upper hand, and she's sure I'm not wearing a wire-and would I wear a wire to admit to sleeping with my partner?-I think she'll jump at the chance. The thought of telling a detective exactly what she did, knowing there's not a thing I can do about it, knowing it must be killing me… It'll be one of the most delicious buzzes of her life. She won't be able to resist."
"She can say whatever she bloody well likes," O'Kelly said. "Without a caution, none of it will be admissible."
"So I'll caution her."
"And you think she'll keep talking? I thought you said the girl's not crazy."
"I don't know," Cassie said. She sounded, just for a second, exhausted and openly pissed off, and it made her seem very young, like a teenager unable to conceal her frustration with the idiotic adult world. "I just think it's our best shot. If we go for a formal interview, she'll be on her guard, she'll sit there and deny everything, and we'll have blown our shot: she'll go home knowing there's no way we can pin anything on her. This way, at least there's a chance she'll figure I can't prove anything and take the risk of talking."
O'Kelly was grating a thumbnail, monotonously and infuriatingly, over the fake-wood grain of the table; he was obviously thinking about it. "If we do it, you wear a wire. I'm not risking this on your word against hers."