There is no mystery. Lee Herdman stormed into a private school just north of Edinburgh and killed two boys. He was a loner, a creep, an army veteran who got kicks out of terrifying local teenagers on his speedboat - just the sort of shady character to commit a random and heinous crime. It's a simple case of a man gone mad.

But how random were the killings at Port Edgar Academy? Why did Herdman open fire only in the student lounge, bypassing the swarm of students outside the school? What exactly was his relationship with the school's misfits? Why are military detectives snooping around the murder scene? And why is the only survivor of the attack, recuperating in the hospital, reluctant to talk?

There is indeed a mystery - only this time, it's why.

When Detective Inspector John Rebus is called out of his jurisdiction to investigate the killings, he is relieved to have the distraction. His entire precinct is abuzz with rumors of his involvement in the death of Martin Fairstone, an ex-con who had been menacing Rebus's partner, Detective Sergeant Siobhan Clarke.

For weeks Fairstone tormented Siobhan: followed her home, left her cryptic messages, even threatened violence. But her woes didn't end when Fairstone died in a fire that consumed his apartment. Now Siobhan has a new worry - the morning after Fairstone's body was found, Rebus appeared with bandages on his severely burned hands. No one, not even Siobhan, can ignore the coincidence.

Immersing himself in the Port Edgar killings does little to help Rebus avoid everyone's suspicion, but an unexpected family tie draws him deeper into the case. With his superiors at police headquarters breathing down his neck, his partner'strust diminishing, and the key witness to the entire private school inquiry staying silent in a hospital bed, Rebus finds himself up against what may become insurmountable odds, asking himself what drives a man to kill - is it a matter of revenge, or a question of blood?