It took her four years. She picked her moment carefully. When she came knocking, it was an early morning in April, a few months after the end of my time in Murder, and I was at the firing range.

The range we use is underground in the city center, deep under half the cars in Dublin and a thick layer of smog. I didn’t need to be there-I’ve always been a good shot, and my next qualifying test wasn’t for months-but for the last while I had been waking up way too early for work and way too restless for anything else, and target practice was the only thing I had found that worked the jitters out of me. I took my time adjusting the earmuffs and checking my gun, waited till everyone else was concentrating on their own targets, so they wouldn’t see me galvanizing like an electrocuted cartoon character on the first few shots. Being easily freaked out comes with its own special skill set: you develop subtle tricks to work around it, make sure people don’t notice. Pretty soon, if you’re a fast learner, you can get through the day looking almost exactly like a normal human being.

I never used to be like that. I always figured nerves were for Jane Austen characters and helium-voiced girls who never buy their round; I would no more have turned shaky in a crisis than I would have carried smelling salts around in my reticule. Getting stabbed by the Drug Demon of UCD barely even fazed me. The department shrink spent weeks trying to convince me I was deeply traumatized, but eventually he had to give up, admit I was fine (sort of regretfully; he doesn’t get a lot of stabbed cops to play with, I think he was hoping I would have some kind of fancy complex) and let me go back to work.

Embarrassingly, the one that got me wasn’t a spectacular mass murder or a hostage crisis gone bad or a nice quiet guy with human organs in his Tupperware. My last case in Murder was such a simple one, so much like dozens of others, nothing to warn us: just a little girl dead on a summer morning, and my partner and me goofing off in the squad room when the call came in. From outside, it even went well. Officially, we got a solve in barely a month, society was saved from the evildoer, it looked all pretty in the media and in the end-of-year stats. There was no dramatic car chase, no shootout, nothing like that; I was the one who came off worst, physically anyway, and all I had was a couple of scratches on my face. They didn’t even leave scars. Such a happy ending, all round.

Underneath, though. Operation Vestal: say it to one of the Murder squad, even now, even one of the guys who don’t know the whole story, and you’ll get that instant look, hands and eyebrows going up meaningfully as he distances himself from the clusterfuck and the collateral damage. In every way that mattered, we lost and we lost big. Some people are little Chernobyls, shimmering with silent, spreading poison: get anywhere near them and every breath you take will wreck you from the inside out. Some cases-ask any cop-are malignant and incurable, devouring everything they touch.

I came out with a variety of symptoms that would have made the shrink bounce up and down in his little leather sandals, except that mercifully it didn’t occur to anyone to send me to the shrink for a scratched face. It was your standard-issue trauma stuff-shaking, not eating, sticking to the ceiling every time the doorbell or the phone rang-with a few ornamentations of my own. My coordination went funny; for the first time in my life I was tripping on my own feet, bumping into doorjambs, bonking my head off cupboards. And I stopped dreaming. Before, I had always dreamed in great wild streams of images, pillars of fire spinning across dark mountains, vines exploding through solid brick, deer leaping down Sandymount beach wrapped in ropes of light; afterwards, I got thick black sleep that hit me like a mallet the second my head touched the pillow. Sam-my boyfriend, although that idea still startled me sometimes-said to give it time, it would all wear off. When I told him I wasn’t so sure, he nodded peacefully and said that would wear off too. Every now and then Sam got right up my nose.

I considered the traditional cop solution-booze, early and often-but I was scared I would end up phoning inappropriate people at three in the morning to spill my guts, plus I discovered that target practice anaesthetized me almost as well and without any messy side effects. This made almost no sense, given the way I was reacting to loud noises in general, but I was OK with that. After the first few shots a fuse would blow in the back of my brain and the rest of the world vanished somewhere faint and far away, my hands turned rock-steady on the gun and it was just me and the paper target, the hard familiar smell of powder in the air and my back braced solid against the recoil. I came out calm and numb as if I’d been Valiumed. By the time the effect wore off, I had made it through another day at work and I could go whack my head off sharp corners in the comfort of my own home. I’d got to the point where I could make nine head shots out of ten, at forty yards, and the wizened little man who ran the range had started looking at me with a horse trainer’s eye and making noises about the department championships.

I finished up around seven, that morning. I was in the locker room, cleaning my gun and trying to shoot the breeze with two guys from Vice without giving them the impression that I wanted to go get breakfast, when my mobile phone rang.

“Jesus,” one of the Vice boys said. “You’re DV, aren’t you? Who has the energy to beat up his missus at this hour?”

“You can always make time for the things that really matter,” I said, digging my locker key out of my pocket.

“Maybe it’s black ops,” said the younger guy, grinning at me. “Looking for sharpshooters.” He was big and redheaded, and he thought I was cute. He had his muscles arranged to full advantage, and I had caught him checking out my ring finger.

“Must’ve heard we weren’t available,” said his mate.

I fished the phone out of my locker. The screen said SAM O’NEILL, and the missed-call icon was flashing at me in one corner.

“Hi,” I said. “What’s up?”

“Cassie,” Sam said. He sounded terrible: breathless and sick, as if someone had punched the wind out of him. “Are you OK?”

I turned my shoulder to the Vice guys and moved off into a corner. “I’m fine. Why? What’s wrong?”

“Jesus Christ,” Sam said. He made a hard little noise like his throat was too tight. “I called you four times. I was about to send someone over to your place looking for you. Why didn’t you answer your bloody phone?”

This was not like Sam. He’s the gentlest guy I’ve ever known. “I’m at the firing range,” I said. “It was in my locker. What’s happened?”

“Sorry. I didn’t mean to… sorry.” He made that harsh little sound again. “I got called out. On a case.”

My heart gave one huge whap against my rib cage. Sam is on the Murder squad. I knew I should probably sit down for this, but I couldn’t make my knees bend. I leaned back against the lockers instead.

“Who is it?” I asked.

“What? No-God, no, it’s not… I mean, it’s not anyone we know. Or anyway I don’t think-Listen, can you come down here?”

My breath came back. “Sam,” I said. “What the hell is going on?”

“Just… can you just come? We’re in Wicklow, outside Glenskehy. You know it, right? If you follow the signs, go through Glenskehy village and keep going straight south, about three-quarters of a mile on there’s a little lane to your right-you’ll see the crime-scene tape. We’ll meet you there.”

The Vice boys were starting to look interested. “My shift starts in an hour,” I said. “It’ll take me that long just to get out there.”

“I’ll call it in. I’ll tell DV we need you.”

“You don’t. I’m not in Murder any more, Sam. If this is a murder case, it’s nothing to do with me.”