“Cassie,” Frank said softly. “Your call.”

For what seemed like a long time, I thought about saying no. Back to DV: the standard Monday crop of the weekend’s aftermath, too many bruises and high-necked sweaters and sunglasses indoors, the regulars filing charges on their boyfriends and withdrawing them by Tuesday night, Maher sitting beside me like a big pink ham in a sweater and sniggering predictably every time we pulled a case with foreign names.

If I went back in there the next morning I would never leave. I knew it solid as a fist in my stomach. This girl was like a dare, flung hard and deadly accurate straight at me: a once-off chance, and catch it if you can.

O’Kelly stretched out his legs and sighed ostentatiously; Cooper examined the cracks in the ceiling. I could tell from the stillness of Sam’s shoulders that he wasn’t breathing. Only Frank was looking at me, his eyes steady and unblinking. The air of the squad room hurt everywhere it touched me. Lexie in dim gold light on the screen was a dark lake I could high-dive into, she was a thin-ice river I could skate away on, she was a long-distance flight leaving now.

“Tell me this woman smoked,” I said.

My ribs opened up like windows, I’d forgotten you could breathe that deeply. "Jesus, you took your time,” said O’Kelly, heaving himself out of his chair and pulling his trousers up over his belly. “I think you’re bloody certifiable, but nothing new there. When you get yourself killed, don’t come crying to me.”

“Fascinating,” Cooper said, eyeing me speculatively; a part of him was obviously working out the odds that I would end up on his table. “Do keep me posted.”

Sam ran a hand over his mouth, hard, and I saw his neck sag. “Marlboro Lights,” Frank said, and hit Eject, a big grin slowly breaking across his face. "That’s my girl.”"

I used to believe, bless my naive little heart, that I had something to offer the robbed dead. Not revenge-there’s no revenge in the world that could return the tiniest fraction of what they’ve lost-and not justice, whatever that means, but the one thing left to give them: the truth. I was good at it. I had one, at least, of the things that make a great detective: the instinct for truth, the inner magnet whose pull tells you beyond any doubt what’s dross, what’s alloy and what’s the pure, uncut metal. I dug out the nuggets without caring when they cut my fingers and brought them in my cupped hands to lay on graves, until I found out-Operation Vestal again-how slippery they were, how easily they crumbled, how deep they sliced and, in the end, how very little they were worth.

In Domestic Violence, if you can get one bruised girl to press charges or go to a shelter, then there’s at least one night when her boyfriend is not going to hit her. Safety is a small debased currency, copper-plated pennies to the gold I had been chasing in Murder, but what value it has it holds. I had learned, by that time, not to take that lightly. A few safe hours and a sheet of phone numbers to call: I had never been able to offer a single murder victim that much.

I had no clue what currency I had to offer Lexie Madison-not safety, obviously, and truth didn’t appear to have been one of her main priorities-but she had come looking for me, alive and dead she had padded closer on soft feet till she arrived with a spectacular bang on my doorstep: she wanted something. What I wanted from her in exchange-I really believed this, at the time-was simple: I wanted her the fuck out of my life. I knew she would drive a hard bargain, but I was good with that; I had done it before.

I don’t tell people this, it’s nobody’s business, but the job is the nearest thing I’ve got to a religion. The detective’s god is the truth, and you don’t get much higher or much more ruthless than that. The sacrifice, at least in Murder and Undercover-and those were always the ones I wanted, why go chasing diluted versions when you could have the breathtaking full-on thing?-is anything or everything you’ve got, your time, your dreams, your marriage, your sanity, your life. Those are the coldest and most capricious gods of the lot, and if they accept you into their service they take not what you want to offer but what they choose.

Undercover picked my honesty. I should have seen this coming, but somehow I had been so caught by the dazzling absoluteness of the job that I had managed to miss the most obvious thing about it: you spend your day lying. I don’t like lying, don’t like doing it, don’t like people who do it, and to me it seemed deeply fucked-up to go after the truth by turning yourself into a liar. I spent months picking my way along a fine double-talk line, cozying up to this small-fish dealer and spinning jokes or sarcasm to mislead him with literal truths. Then one day he fried both his brain cells on speed, pulled a knife on me and asked me if I was just using him to get to know his supplier. I skated the fine line for what felt like hours-Chill out, what’s your problem, what have I ever done to make you think I’m trying to screw you over?-stalling and hoping to God that Frank was listening to the mike feed. Dealer Boy put the knife in between my ribs and shrieked in my face, Are you? Are you? No bullshit. Yes or no. Are you? When I hesitated-because of course I was, even if it wasn’t for the reason he had in mind, and this seemed like too crucial a moment for lies-he stabbed me. Then he burst into tears, and sometime in there Frank arrived and carted me discreetly off to the hospital. But I knew. The sacrifice had been demanded and I had withheld it. I had thirty stitches for warning: Don’t do that again.

I was a good Murder detective. Rob once told me that all through his first case he had elaborate visions of fucking up, sneezing on DNA evidence, waving a cheerful good-bye to someone who had just let slip the giveaway piece of withheld info, bumbling vacantly past every clue and red flag. I never had that. My first Murder case was about as banal and depressing as they get-a young junkie knifed in the stairwell of a nightmare block of flats, great blood smears down grimy flights of stairs and eyes watching behind chained doors and the smell of piss everywhere. I stood on the landing with my hands in my pockets so I wouldn’t touch anything by mistake, looking up at the victim sprawled on the steps with his tracksuit bottoms half pulled down by the fall or the fight, and I thought: So this is it. This is where I was coming to, all along.

I still remember that junkie’s face: too thin, a faint fuzz of pale stubble, his mouth a little open as if all this had startled him silly. He had a crooked front tooth. Against all the odds and O’Kelly’s nonstop depressing predictions, we got a solve.

On Operation Vestal the Murder god chose my best friend and my honesty, and gave me nothing in exchange. I transferred out knowing there would be a price to pay for the desertion. At the back of my mind I expected my solve rate to plummet, expected every vicious guy to beat the living daylights out of me, every raging woman to scratch my eyes out. I wasn’t scared; I was looking forward to it being over. But when nothing happened I realized, like a slow cold tide, that this was the punishment: to be turned loose, allowed to go on my way. To be left empty by my guardian god.

And then Sam phoned and Frank was waiting at the top of the hill, and strong implacable hands were reeling me back in. You can put all of this down to a superstitious streak if that’s easiest, or to the kind of intense secret life that a lot of orphans and onlies have; I don’t mind. But maybe it goes some way towards explaining why I said yes to Operation Mirror, and why, when I signed on, I figured there was a decent chance I was going to get killed.