Our timing was a little off: Cooper was just coming out of the autopsy room in his green scrubs, a waterproof gown held away from him between finger and thumb. "Detectives," he said, raising his eyebrows. "What a surprise. If only you'd let me know you were planning to come, I would of course have waited until you managed to fit us in."

He was being snotty because we were too late for the post-mortem. It was, in all fairness, not even eleven o'clock, but Cooper gets into work between six and seven, leaves by three or four, and likes you to remember it. His morgue assistants all hate him for this, which doesn't bother him because he mostly hates them, too. Cooper prides himself on instant, unpredictable dislikes; as far as we've been able to figure out so far, he dislikes blond women, short men, anyone with more than two earrings and people who say "you know" too much, as well as various random people who don't fit into any of these categories. Fortunately he had decided to like me and Cassie, or he would have made us go back to work and wait until he sent over the post-mortem results (handwritten-Cooper writes all his reports in spidery fountain pen, an idea I sort of like but don't have the courage to try out in the squad room). There are days when I worry, secretly, that in a decade or two I might wake up and discover I've turned into Cooper.

"Wow," Sam said, trying. "Finished already?" Cooper gave him a chilly glance.

"Dr. Cooper, I'm so sorry to burst in on you at this hour," Cassie said. "Superintendent O'Kelly wanted to go over a few things, so we had a hard time getting away." I nodded wearily and raised my eyes to the ceiling.

"Ah. Well, yes," Cooper said. His tone implied that he found it slightly tasteless of us to mention O'Kelly at all.

"If by any chance you have a few moments," I said, "would you mind talking us through the results?"

"But of course," Cooper said, with an infinitesimal, long-suffering sigh. Actually, like any master craftsman, he loves showing off his work. He held the autopsy-room door open for us and the smell hit me, that unique combination of death and cold and rubbing alcohol that sends an instinctive animal recoil through you every time.

Bodies in Dublin go to the city morgue, but Knocknaree is outside the city limits; rural victims are simply brought to the nearest hospital, and the post-mortem is done there. Conditions vary. This room was windowless and grubby, layers of grime on the green floor-tiles and nameless stains in the old porcelain sinks. The two autopsy tables were the only things in the room that looked post-1950s; they were bright stainless steel, light flaring off those grooved edges.

Katy Devlin was naked under the merciless fluorescent lights and too small for the table, and she looked somehow much deader than she had the previous day; I thought of the old superstition that the soul lingers near the body for a few days, bewildered and unsure. She was gray-white, like something out of Roswell, with dark blotches of lividity down her left side. Cooper's assistant had already sewn her scalp back together, thank God, and was working on the Y incision across her torso, big sloppy stitches with a needle the size of a sailmaker's. I felt a momentary, crazy pang of guilt at being late, at leaving her all on her own-she was so small-through this final violation: we should have been there, she should have had someone to hold her hand while Cooper's detached, gloved fingers prodded and sliced. Sam, to my surprise, crossed himself unobtrusively.

"Pubescent white female," Cooper said, brushing past us to the table and motioning the assistant away, "aged twelve, so I'm told. Height and weight both on the low side, but within normal limits. Scars indicating abdominal surgery, possibly an exploratory laparotomy, some time ago. No obvious pathology; as far as I can tell, she died healthy, if you'll pardon the oxymoron."

We clustered around the table like obedient students; our footsteps threw small flat echoes off the tiled walls. The assistant leaned against one of the sinks and folded his arms, chewing stolidly on a piece of gum. One arm of the Y incision still gaped open, dark and unthinkable, the needle stuck casually through a flap of skin for safekeeping.

"Any chance of DNA?" I asked.

"One step at a time, if you please," Cooper said fussily. "Now. There were two blows to the head, both ante-mortem-before death," he added sweetly to Sam, who nodded solemnly. "Both were struck with a hard, rough object with protrusions but no distinct edges, consistent with the rock Ms. Miller presented to me for inspection. One was a light blow to the back of the head, near the crown. It caused a small area of abrasion and some bleeding, but no cracks to the skull." He turned Katy's head to one side, to show us the little bump. They had cleaned the blood off her face, to check for any injuries underneath, but there were still faint swipes of it across her cheek.

"So maybe she dodged, or she was running away from him while he was swinging," Cassie said.

We don't have profilers. When we really need one we bring one over from England, but most of the time a lot of the Murder guys just use Cassie, on the dubious basis that she studied psychology at Trinity for three and a half years. We don't tell O'Kelly this-he considers profilers to be one step up from psychics, and only grudgingly lets us listen even to the English guys-but I think she's probably fairly good at it, although presumably this is for reasons unrelated to her years of Freud and lab rats. She always comes up with a couple of useful new angles, and usually turns out to be quite close to the mark.

Cooper took his time thinking about it, to punish her for interrupting. Finally he shook his head judiciously. "I consider that unlikely. Had she been moving when this blow was struck, one would expect peripheral grazing, but there was none. The other blow, in contrast…" He tilted Katy's head to the other side and hooked back her hair with one finger. On her left temple a patch of skin had been shaved to expose a wide, jagged laceration, splinters of bone poking out. Someone, Sam or Cassie, swallowed.

"As you see," Cooper said, "the other blow was far more forceful. It landed just behind and above the left ear, causing a depressed skull fracture and a sizable subdural hematoma. Here and here"-he flicked his finger-"you'll observe the peripheral grazing to which I referred, at the proximal edge of the primary impact point: as the blow was struck, she appears to have turned her head away, so the weapon skidded along her skull briefly before achieving its full impact. Do I make myself clear?"

We all nodded. I glanced covertly across at Sam and was heartened by the fact that he looked like he was having a hard time, too.

"This blow would have been sufficient to cause death within hours. However, the hematoma had progressed very little, so we can safely say that she died of other causes within a short time of receiving this injury."

"Can you tell whether she was facing towards him or away from him?" Cassie asked.

"The indications are that she may have been prone when the harder blow was struck: there was considerable bleeding, and the flow was directed inwards across the left side of the face, with some pooling apparent around the central line of the nose and mouth." This was good news, if I can use the term at all in this context: there would be blood at the scene, if we ever found it. Also, it meant we were probably looking for someone left-handed, and, while this wasn't Agatha Christie and real cases seldom hinge on that kind of thing, at this point any tiny lead was an improvement.

"There was a struggle-prior to this blow, I may add: it would have rendered her unconscious immediately. There are defensive wounds to the hands and forearms-bruising, abrasions, three broken fingernails on the right hand-probably inflicted by the same weapon as she warded off blows." He lifted one of her wrists between finger and thumb, turned over her arm to show us the scrapes. Her fingernails had been clipped off short and taken away for analysis; on the back of her hand was a stylized flower with a smiley face in the middle, drawn in faded marker. "I also found bruising around the mouth and toothmarks on the insides of the lips, consistent with the perpetrator pressing a hand over her mouth."