Knots and Crosses (Inspector Rebus #1) by Ian Rankin

Detective John Rebus: His city is being terrorized by a baffling series of murders...and he's tied to a maniac by an invisible knot of blood. Once John Rebus served in Britain's elite SAS. Now he's an Edinburgh cop who hides from his memories, misses promotions and ignores a series of crank letters. But as the ghoulish killings mount and the tabloid headlines scream, Rebus cannot stop the feverish shrieks from within his own mind.