"I don't think you need to be too worried about her," Cassie said. She finished her wine. "We could be completely wrong about Katy; it's all guesswork. And I wouldn't put too much weight on anything Cathal Mills says. He strikes me as a psychopath, and they lie easier than they tell the truth."

I raised my eyebrows. "You only met him for about five minutes. What, you're diagnosing the guy? He just struck me as a prick."

She shrugged. "I'm not saying I'm sure about Cathal. But they're surprisingly easy to spot, if you know how."

"Is this what they taught you at Trinity?"

Cassie held out her hand for my glass, got up to refill them. "Not exactly," she said, at the fridge. "I knew a psychopath once."

Her back was to me, and if there was an odd undertone in her voice I didn't catch it. "I did see this thing on the Discovery Channel where they said up to five percent of the population are psychopaths," I said, "but most of them don't break the law so they never get diagnosed. How much would you bet that half the government-"

"Rob," Cassie said. "Shut up. Please. I'm trying to tell you something here."

This time I did hear the strain. She came over and gave me my glass, took hers to the window and leaned back on the sill. "You wanted to know why I dropped out of college," she said, very evenly. "In second year I made friends with this guy in my class. He was popular, quite good-looking and very charming and intelligent and interesting-I didn't fancy him or anything like that, but I guess I was flattered that he was paying all this attention to me. We used to skip all our classes and spend hours over coffee. He brought me presents-cheap ones, and some of them looked used, but we were broke students, and hey, it's the thought that counts, right? Everyone thought it was sweet, how close we were."

She took a sip of her drink, swallowed hard. "I worked out pretty fast that he told a lot of lies, mostly for no real reason, but I knew-well, he'd told me-that he'd had a terrible childhood and that he'd been bullied in school, so I figured he'd got into the habit of lying to protect himself. I thought-Jesus Christ-I thought I could help: if he knew he had a friend who'd stick by him no matter what, he'd get more secure and wouldn't need to lie any more. I was only eighteen, nineteen."

I was afraid to move, even to put down my glass; I was terrified that any tiny movement would be the one that would send her pushing herself up off the windowsill and spinning the subject away with some flippant comment. There was an odd, taut set to her mouth that made her look much older, and I knew she had never told this story to anyone, ever before.

"I didn't even notice I was drifting away from all the other friends I'd made, because he went into this cold sulk if I spent time with them. He went into the cold sulk a lot, actually, for any reason or none, and I would have to spend ages trying to figure out what I'd done and apologizing and making up for it. When I went to meet him I never knew whether he'd be all hugs and compliments or all cold shoulder and disapproving looks; there was no logic to it. Sometimes the things he pulled-just little things: borrowing my lecture notes just before exams, then forgetting to bring them back in for days, then claiming he'd lost them, then getting outraged when I saw them sticking out of his bag, that kind of thing-it made me so furious I wanted to kill him with my bare hands, but he was lovely just often enough that I didn't want to stop hanging around with him." A tiny, crooked twist of a smile. "I didn't want to hurt him."

It took her three tries to light a cigarette; Cassie, who had told me about getting stabbed without so much as tensing up. "Anyway," she said, "this went on for almost two years. In January of fourth year he made a pass at me, in my flat. I turned him down-I have no idea why, by that time I was so confused I barely knew what I was doing, but thank God I had a few of my instincts left. I said I just wanted to be friends, he seemed fine with it, we talked for a while, he left. The next day I went into class and everyone was staring at me and nobody would talk to me. It took me two weeks to find out what was going on. I finally cornered this girl Sarah-Jane-we'd been pretty good friends, back in first year-and she said that they all knew what I'd done to him."

She drew on her cigarette, hard and fast. She was looking at me, but not quite meeting my eyes; hers were too wide, dilated. I thought of Jessica Devlin's dazed, narcotized stare. "The night I turned him down, he'd gone straight to these other girls' flat, girls from our class. He arrived in tears. He told them that he and I had been secretly going out for a while, that he'd decided it wasn't working out, and that I had said if he broke up with me I'd tell everyone he'd raped me. He said I'd threatened to go to the police, the papers, to ruin his life." She looked for an ashtray, flicked ash, missed.

It didn't occur to me at the time to wonder why she was telling me this story, why now. This may seem strange, but everything did that month, strange and precarious. The moment when Cassie had said, "We'll have it," had set in motion some unstoppable tectonic shift; familiar things were cracking open and twisting inside out before my eyes, the world turning beautiful and dangerous as a bright spinning blade. Cassie opening the door to one of her secret rooms seemed like a natural, inevitable part of this massive sea change. In a way, I suppose it was. It was only much later that I understood she had actually been telling me something very specific, if I had just been paying attention.

"My God," I said, after a while. "Just because you bruised his ego?"

"Not just that," Cassie said. She was wearing a soft cherry-colored sweater and I could see it vibrating, very fast, just above her breast, and I realized my heart was speeding, too. "Because he was bored. Because, by turning him down, I had made it clear that he'd got as much entertainment out of me as he was going to, so this was the only other use he had for me. Because, when you come right down to it, it was fun."

"Did you tell this Sarah-Jane what had happened?"

"Oh, yeah," Cassie said levelly. "I told everyone who would still talk to me. Not one of them believed me. They all believed him-all our classmates, all our mutual acquaintances, which added up to just about everyone I knew. People who were supposed to be my friends."

"Oh, Cassie," I said. I was aching to go over to her, put my arms around her, hold her close until that terrible rigidity melted out of her body and she came back from whatever remote place she had gone to. But the immobility of her, her braced shoulders: I couldn't tell whether she would welcome it or whether it would be the worst thing I could do. Blame boarding school; blame, if you prefer, some deep-seated character flaw. The fact is that I didn't know how. I doubt that, in the long run, it would have made any difference; but this only makes me wish even more intensely that, at least for that one moment, I had known what to do.

"I stuck it out for another couple of weeks," Cassie said. She lit another cigarette off the end of the old one, something I had never seen her do before. "He was always surrounded by this knot of people giving him protective pats and glaring at me. People were coming up to me to tell me that I was the reason why genuine rapists got away with it. One girl said I deserved to be raped so I'd realize what a horrible thing I'd done."

She laughed, a small harsh sound. "It's ironic, isn't it? A hundred psychology students, and not one of us recognized a classic psychopath. You know the strange thing? I wished I had done everything he claimed I had. If I had, then it would all have made sense: I would have been getting what I deserved. But I hadn't done any of it, and yet that made absolutely no difference to what happened. There was no such thing as cause and effect. I thought I was losing my mind."