Given his contempt for authority, his tendency to pursue investigative avenues of his own choosing, and his habitually ornery manner, it's a wonder that John Rebus hasn't been booted unceremoniously from his job as an Edinburgh cop. He certainly tempts that fate again in A Question of Blood, which finds him and his younger partner, Detective Sergeant Siobhan Clarke, trying to close the case of a withdrawn ex-soldier named Lee Herdman, who apparently shot three teenage boys at a Scottish private school, leaving two of them dead, before turning the pistol on himself. "There’s no mystery," Siobhan insists at the start of this 14th Rebus novel (following Resurrection Men). "Herdman lost his marbles, that’s all." However, the hard-drinking, chain-smoking Rebus, who'd once sought entry into the same elite regiment in which Herdman served (but ultimately cracked under psychological interrogation), thinks there's more motive than mania behind this classroom slaughter. Perhaps something to do with the gunman's role in a 1995 mission to salvage a downed military helicopter, or with Teri Cotter, a 15-year-old "Goth" who broadcasts her bedroom life over the Internet, yet keeps private her relationship with the haunted Herdman. Rebus's doubts about the murder-suicide theory are deepened with the appearance of two tight-lipped army investigators, and by the peculiar behavior of James Bell, the boy who was only wounded during Herdman's firing spree and whose politician father hopes to use that tragedy as ammo in the campaign against widespread gun ownership. But the detective inspector's focus on this inquiry is susceptible to diversion, both by an internal police probe into his role in the burning death of a small-time crook who'd been stalking Siobhan, and by the fact that Rebus--who shies away from any family contacts--was related to one of Herdman’s victims. Now middle-aged and on the downward slope of his pugnacity (the high point may have come in 1997's Black and Blue), Rebus has become the engine of his own obsolescence. Overexposure to criminals has left him better at understanding them than his colleagues, and he only worsens his career standing by fighting other people's battles for them, especially Siobhan, who risks learning too many lessons from her mentor. To watch Rebus subvert police conventions and fend of personal demons (that latter struggle mirrored in A Question of Blood by Herdman's own) is worth the admission to this consistently ambitious series. --J. Kingston Pierce