How can I ever make you understand Cassie and me? I would have to take you there, walk you down every path of our secret shared geography. The truism says it's against all the odds for a straight man and woman to be real friends, platonic friends; we rolled thirteen, threw down five aces and ran away giggling. She was the summertime cousin out of storybooks, the one you taught to swim at some midge-humming lake and pestered with tadpoles down her swimsuit, with whom you practiced first kisses on a heather hillside and laughed about it years later over a clandestine joint in your granny's cluttered attic. She painted my fingernails gold and dared me to leave them that way for work. I told Quigley that she thought Croke Park Stadium should be turned into a shopping center, and watched her try to decipher his outraged splutter. She cut up the packaging of her new mouse mat and stuck the part that said TOUCH ME-FEEL THE DIFFERENCE to the back of my shirt, and I wore it half the day before I noticed. We climbed out her window and down the fire escape and lay on the roof of the extension below, drinking improvised cocktails and singing Tom Waits and watching the stars spin dizzily around us.

No. These are stories I like to think about, small bright currency and not without value; but above all that, and underlying everything we did, she was my partner. I don't know how to tell you what that word, even now, does to me; what it means. I could tell you about going room by room, guns two-handed at arm's length, through silent houses where a suspect could be armed and waiting behind any door; or about long nights on surveillance, sitting in a dark car drinking black coffee from a thermos and trying to play gin rummy by the light of a streetlamp. Once we chased two hit-and-run joyriders through their own territory-graffiti and rubbish-dump wastelands whipping past the windows, sixty miles per hour, seventy, I floored it and stopped looking at the speedometer-until they spun into a wall, and then we held the sobbing fifteen-year-old driver between us, promising him that his mother and the ambulance would be there soon, while he died in our arms. In a notorious tower block that would redraw the outlines of your image of humanity, a junkie pulled a syringe on me-we weren't even interested in him, it was his brother we were after, and the conversation had seemed to be proceeding along normal lines until his hand moved too fast and suddenly there was a needle against my throat. While I stood frozen and sweating and wildly praying that neither of us would sneeze, Cassie sat down cross-legged on the reeking carpet, offered the guy a cigarette and talked to him for an hour and twenty minutes (in the course of which he demanded, variously, our wallets, a car, a fix, a Sprite and to be left alone); talked to him so matter-of-factly and with such frank interest that finally he dropped the syringe and slid down the wall to sit across from her, and he was starting to tell her his life story when I got my hands under control enough to slap the cuffs on him.

The girls I dream of are the gentle ones, wistful by high windows or singing sweet old songs at a piano, long hair drifting, tender as apple blossom. But a girl who goes into battle beside you and keeps your back is a different thing, a thing to make you shiver. Think of the first time you slept with someone, or the first time you fell in love: that blinding explosion that left you crackling to the fingertips with electricity, initiated and transformed. I tell you that was nothing, nothing at all, beside the power of putting your lives, simply and daily, into each other's hands.

That weekend I went over to my parents' house for Sunday dinner. I do this every few weeks, although I'm not really sure why. We're not close; the best we can do is a mutual state of amicable and faintly puzzled politeness, like people who met on a package tour and can't figure out how to end the connection. Sometimes I bring Cassie with me. My parents love her-she teases my father about his gardening, and sometimes when she helps my mother in the kitchen I hear my mother laugh, full-throated and happy as a girl-and drop hopeful little hints about how close we are, which we cheerfully ignore.

"Where's Cassie today?" my mother asked after dinner. She had made macaroni and cheese-she has some idea that this is my favorite dish (which it may well have been, at some point in my life) and she cooks it, as a small timid expression of sympathy, whenever something in the papers indicates that a case of mine isn't going well. Even the smell of it makes me claustrophobic and itchy. She and I were in the kitchen; I was washing up and she was drying. My father was in the sitting room, watching a Columbo movie on TV. The kitchen was dim and we had the light on, though it was only midafternoon.

"I think she went to her aunt and uncle's," I said. Actually, Cassie was probably curled up on her sofa, reading and eating ice cream out of the carton-we hadn't had much time to ourselves, the last couple of weeks, and Cassie, like me, needs a certain amount of solitude-but I knew it would upset my mother, the thought of her spending a Sunday alone.

"That'll be nice for her: being looked after. The pair of you must be shattered."

"We're pretty tired," I said.

"All that back and forth to Knocknaree."

My parents and I don't talk about my work, except in the most general terms, and we never mention Knocknaree. I looked up sharply, but my mother was tilting a plate to the light to look for wet streaks.

"It's a long drive, all right," I said.

"I read in the paper," my mother said carefully, "that the police were talking to Peter and Jamie's families again. Was that yourself and Cassie?"

"Not the Savages. I talked to Ms. Rowan, though, yes. Does this look clean to you?"

"It's grand," my mother said, taking the baking dish out of my hand. "How's Alicia now?"

There was something in her voice that made me look up again, startled. She caught my gaze and flushed, wiping hair away from her cheek with the back of her wrist. "Ah, we used to be great friends. Alicia was…well, I suppose she was almost like a little sister to me. We got out of touch, after. I was just wondering how she was, is all."

I had a fast, queasy flash of retrospective panic: if I had known that Alicia Rowan and my mother had been close, I would never have gone near that house. "I think she's all right," I said. "As much as one could expect. She still has Jamie's room the way it was."

My mother clicked her tongue unhappily. We washed up in silence for some time: clink of cutlery, Peter Falk cunningly interrogating someone in the next room. Outside the window, a pair of magpies landed on the grass and started picking over the tiny garden, discussing it raucously as they went.

"Shoo," my mother said automatically, rapping the glass, and sighed. "I suppose I've never forgiven myself for losing touch with Alicia. She'd no one else. She was such a sweet girl, a real innocent-she was still hoping Jamie's father would leave his wife, after all that time, and they'd be a family… Did she ever marry?"

"No. But she doesn't seem unhappy, really. She teaches yoga." The suds in the basin had turned lukewarm and clammy; I reached for the kettle and added more hot water.

"That's one reason we moved away, you know," my mother said. She had her back to me, sorting cutlery into a drawer. "I couldn't face them-Alicia and Angela and Joseph. I had my son back safe and sound, and they were going through hell… I could hardly go out of the house, in case I'd meet them. I know it sounds mad, but I felt guilty. I thought they must hate me for having you safe. I don't see how they could help it."