"Gee, you think?" she said, and started to laugh. After a moment I joined in. The mole thing bothered me-if anyone actually believed it, they would never tell me anything again-and being taken for English infuriates me to an irrational degree, but I sort of enjoyed the absurd idea of me as James Bond.

"I'm from Dublin ," I said. "I got the accent at boarding school in England. And that lobotomized bogger knows it." Which he did; in my first weeks on the squad he had pestered me so monotonously about what an English guy was doing in the Irish police force, like a child poking you in the arm and droning "Why? Why? Why?" that I had finally broken my need-to-know rule and explained the accent. Apparently I should have used smaller words.

"What are you doing working with him?" Cassie asked.

"Quietly losing my mind," I said.

Something, I'm still not sure what, had made up Cassie's mind. She leaned sideways, switching her mug to the other hand (she swears we were drinking coffee by that stage and claims that I only think it was hot whiskey because we drank it so often that winter, but I know, I remember the sharp prongs of a clove on my tongue, the heady steam), and pulled up her top to just under her breast. I was so startled that it took me a moment to realize what she was showing me: a long scar, still red and raised and spidered with stitch marks, curving along the line of a rib. "I got stabbed," she said.

It was so obvious that I was embarrassed nobody had thought of it. A detective wounded on duty gets his or her choice of assignment. I suppose we had overlooked this possibility because normally a stabbing would have practically shorted out the grapevine; we had heard nothing about this.

"Jesus," I said. "What happened?"

"I was undercover in UCD," Cassie said. This explained both the clothes and the information gap-undercover are serious about secrecy. "That's how I made detective so fast: there was a ring dealing on campus, and Drugs wanted to find out who was behind it, so they needed people who could pass for students. I went in as a psychology postgrad. I did a few years of psychology at Trinity before Templemore, so I could talk the talk, and I look young."

She did. There was a specific clarity about her face that I've never seen in anyone else; her skin was poreless as a child's, and her features-wide mouth, high round cheekbones, tilted nose, long curves of eyebrow-made other people's look smudged and blurry. As far as I could tell she never wore makeup, except for a red-tinted lip balm that smelled of cinnamon and made her seem even younger. Few people would have considered her beautiful, but my tastes have always leaned toward bespoke rather than brand name, and I took far more pleasure in looking at her than at any of the busty blond clones whom magazines, insultingly, tell me I should desire.

"And your cover got blown?"

"No," she said, indignant. "I found out who the main dealer was-this brain-dead rich boy from Blackrock, studying business, of course-and I spent months making friends with him, laughing at his crap jokes, proofreading his essays. Then I suggested maybe I could deal to the girls, they'd be less nervous about buying drugs from another woman, right? He liked the idea, everything was going great, I was dropping hints that maybe it would be simpler if I met the supplier myself instead of getting the stuff through him. Only then Dealer Boy started snorting a little too much of his own speed-this was in May, he had exams coming up. He got paranoid, decided I was trying to take over his business and stabbed me." She took a sip of her drink. "Don't tell Quigley, though. The operation's still going on, so I'm not supposed to talk about it. Let the poor little fucker enjoy his illusions."

I was secretly terribly impressed, not only by the stabbing (after all, I told myself, it wasn't as though she had done something outstandingly brave or intelligent; she had just failed to dodge fast enough), but by the dark, adrenaline-paced thought of undercover work and by the utter casualness with which she told the story. Having worked hard to perfect an air of easy indifference, I recognize the real thing when I see it.

"Jesus," I said again. "I bet he got a good going-over when they brought him in." I've never hit a suspect-I find there's no need to, as long as you make them think you might-but there are guys who do, and anyone who stabs a cop is likely to pick up a few bruises en route to the station.

She cocked an eyebrow at me, amused. "They didn't. That would've wrecked the whole operation. They need him to get to the supplier; they just started over with a new undercover."

"But don't you want him taken down?" I said, frustrated by her calm and by my own creeping sense of naïveté. "He stabbed you."

Cassie shrugged. "After all, if you think about it, he had a point: I was only pretending to be his friend to screw him over. And he was a strung-out drug dealer. That's what strung-out drug dealers do."

After that my memory grows hazy again. I know that, determined to impress her in my turn, and never having been stabbed or involved in a shootout or anything, I told her a long and rambling and mostly true story about talking down a guy who was threatening to jump off the roof of a block of flats with his baby, back when I was in Domestic Violence (really, I think I must have been a little drunk: another reason I'm so sure we had hot whiskey). I remember a passionate conversation about Dylan Thomas, I think, Cassie kneeling up on the sofa and gesturing, her cigarette burning away forgotten in the ashtray. Bantering, smart but tentative as shy circling children, both of us checking covertly after each riposte to make sure we hadn't crossed any line or hurt any feelings. Firelight and the Cowboy Junkies, Cassie singing along in a sweet rough undertone.

"The drugs you got from Dealer Boy," I said, later. "Did you actually sell them to students?"

Cassie got up to put on the kettle. "Occasionally," she said.

"Didn't that bother you?"

"Everything about undercover bothered me," Cassie said. "Everything."

When we went into work the next morning we were friends. It really was as simple as that: we planted seeds without thinking, and woke up to our own private beanstalk. At break time I caught Cassie's eye and mimed a cigarette, and we went outside to sit cross-legged at either end of a bench, like bookends. At the end of the shift she waited for me, bitching to the air about how long I took to get my things together ("It's like hanging out with Sarah Jessica Parker. Don't forget your lip liner, sweetie, we don't want the chauffeur to have to go back for it again"), and said "Pint?" on the way down the stairs. I can't explain the alchemy that transmuted one evening into the equivalent of years held lightly in common. The only way I can put it is that we recognized, too surely even for surprise, that we shared the same currency.

As soon as she finished learning the ropes with Costello, we partnered up. O'Kelly put up a bit of a fight-he didn't like the idea of two shiny new rookies working together, and it meant he would have to find something else to do with Quigley-but I had, by sheer luck rather than shrewd detection, found someone who had heard someone bragging about killing the homeless guy, so I was in O'Kelly's good books, and I took full advantage of it. He warned us that he would give us only the simplest cases and the nohopers, "nothing that needs real detective work," and we nodded meekly and thanked him again, aware that murderers aren't considerate enough to ensure that the complex cases come up in strict rotation. Cassie moved her stuff to the desk beside mine, and Costello got stuck with Quigley and gave us sad reproachful looks for weeks, like a martyred Labrador.