“She’s having a flying lesson this afternoon.”

“Really?” Duff raised an eyebrow. “That doesn’t come cheap.”

“I think it’s a freebie, courtesy of a guy who owns an airfield and a Jag.”

“Brimson?” Hogan guessed. Rebus nodded.

“My offer to her of a ride in my MG pales by comparison,” Duff grumbled.

“You can’t compete with this guy. He’s got one of those corporate jets.”

Duff whistled. “Must be loaded, then. Those can set you back a few mil.”

“Aye, right,” Rebus said dismissively.

“I’m serious,” Duff said. “And that’s secondhand.”

“You mean millions of pounds?” This from Bobby Hogan. Duff nodded. “Business must be good, eh?”

Yes, Rebus was thinking, so good Brimson could afford a day off for a trip to Jura…

“Here we go,” Duff was saying, drawing their attention back to the laptop. “Basically, this has everything I need.” He ran an admiring finger along the edge of the screen. “There’s a simulation we can run… shows the pattern you’d expect to get when a gun is fired from whatever distance, whatever angle to the head or body.” He clicked a few more buttons and Rebus heard the whirr of the laptop’s CD drive. The graphics appeared, a skeletal figure standing sideways to a wall. “See here?” Duff was saying. “Subject is twenty centimeters from the wall, bullet is fired from a distance of two meters… entry and exit and… boom!” They watched as a line seemed to enter the skull, reappearing as a fine speckling. Duff’s finger moved across the touch pad, highlighting the marked area of wall, which then was magnified on-screen.

“Gives us a pretty good picture,” he said with a smile.

“Ray,” Hogan said quietly, “just so you know, DI Rebus here lost a family member in that room.”

Duff’s smile melted away. “I didn’t mean to make light of…”

“Maybe if we could just cut to the chase,” Rebus replied coolly. He didn’t blame Duff: how could he? The man hadn’t known. But anything to speed things up.

Duff plunged his hands into the pockets of his white lab coat and turned towards the photographs.

“We need to look at these now,” he said, eyes on Rebus.

“That’s fine,” Rebus agreed with a nod. “Let’s just get it done, eh?”

The early animation had left Duff’s voice when he spoke now. “First victim was the one nearest the door. That was Anthony Jarvies. Herdman walks in and aims at the person nearest him-stands to reason. From the evidence, the two were just under two meters apart. No real sense of an angle… Herdman was about the same height as his victim, so the bullet takes a lateral path through the skull. Blood spatter pattern is pretty much what we’d expect to find. Then Herdman turns. Second victim is a little farther away, maybe three meters. Herdman may have closed that gap before firing, but probably not by much. This time the bullet angles down through the skull, indicating that Derek Renshaw was maybe trying to duck out of the way.” He looked at his audience. “With me so far?” Rebus and Hogan nodded, and the three men moved along the wall. “Blood stains on the floor are explicable, nothing out of place.” Duff paused.

“Until now?” Rebus guessed. The scientist nodded.

“We’ve got a lot of data on firearms, what sort of damage they do to the human body and to anything else they come in contact with…”

“And James Bell is proving a puzzle?”

Duff nodded. “A bit of a puzzle, yes.”

Hogan looked from Duff to Rebus and back again. “How so?”

“In Bell’s statement he says he was hit while in movement. Basically, he was diving for the floor. He seemed to think this might explain why he wasn’t killed. He also said that Herdman was about three and a half meters away when he fired.” He crossed to the computer again, and brought a 3-D simulation onto the screen, showing the classroom and pointing to the positions of gunman and schoolboy. “Again, the victim is of similar height to Herdman. But this time, the angle of the shot appears to be upwards.” Duff paused to let this sink in. “As if the person doing the firing was the one crouching down.” He bent low at the knees and pointed an imaginary pistol, then straightened and crossed to another of the benches. There was a light box sitting on it, and he switched it on, illuminating a set of X-rays showing the route the bullet had taken in ripping through James Bell’s shoulder. “Entry wound at the front, exit at the back. You can see the trajectory quite clearly.” He traced it for them with his finger.

“So Herdman was crouching down,” Bobby Hogan said, with a shrug of the shoulders.

“I get the feeling Ray’s just warming up,” Rebus said quietly, thinking that he wouldn’t have too many questions for the scientist after all.

Duff returned Rebus’s look and went back to the photographs. “No blood spatter pattern,” he said, circling the area of the wall. Then he held up a hand. “Actually, that’s not strictly true. There’s blood present, but it’s such a fine diffusion you can’t really make it out.”

“Meaning what?” Hogan asked, not bothering to hide his impatience.

“Meaning James Bell wasn’t standing where he said he was at the time he was shot. He was much farther into the room, which means closer to Herdman.”

“Yet there’s still that upward trajectory to the shot?” Rebus noted.

Duff nodded, then pulled open a drawer and brought out a bag. It was clear polyethylene, edged with brown paper. An evidence bag. Folded up inside lay a bloodstained white shirt, the bullet hole at the shoulder clearly visible.

“James Bell’s shirt,” Duff stated. “And here we find something else…”

“Powder burns,” Rebus said quietly. Hogan turned to him.

“How come you already know all this?” he hissed.

Rebus shrugged. “I’ve got no social life, Bobby. Nothing to do with myself but sit and think about things.” Hogan glowered, letting Rebus know this was well short of an acceptable answer.

“DI Rebus is spot on,” Duff said, gaining their attention again. “You wouldn’t expect powder burns on the bodies of the first two victims. They were shot from a distance. You only get powder burns when the gun is close to the skin or, say, the victim’s clothes…”

“Did Herdman himself have powder burns?” Rebus asked.

Duff nodded. “Consistent with placing the pistol to his temple and firing.”

Rebus went back along the display of photos, taking his time. They weren’t really telling him anything, which in a way was the whole point. You had to peer beneath their surface to begin to glimpse the truth. Hogan was scratching the nape of his neck.

“I’m not really getting this,” he said.

“It’s a puzzle,” Duff agreed. “Hard to square the witness’s account with the evidence.”

“Depends which way you look at it, though, Ray, am I right?”

Duff fixed eyes with Rebus and nodded. “There’s always a way to explain things.”

“Take your time, then.” Hogan slapped his hands down on the workbench. “I had nothing better to do with myself today anyway.”

“Just got to look at it a different way, Bobby,” Rebus told him. “James Bell was shot at point-blank range…”

“By someone the approximate size of a garden gnome,” Hogan said dismissively.

Rebus shook his head. “It’s just that Herdman couldn’t have done it.”

Hogan’s eyes widened. “Wait a second…”

“Isn’t that right, Ray?”

“It’s one conclusion, certainly.” Duff was rubbing the underside of his jaw.

“Couldn’t have done it?” Hogan echoed. “You’re saying there was someone else in there? An accomplice?”

Rebus shook his head. “I’m saying it’s possible-maybe even probable-that Lee Herdman only killed one person in that room.”

Hogan’s eyes narrowed. “And who would that be?”

Rebus turned his attention to Ray Duff, who supplied the answer.

“Himself,” Duff stated, as though it were the simplest explanation in the world.