Let It Bleed by Ian Rankin (Inspector Rebus #7)

Detective John Rebus understands that murder is usually very simple. Passion and greed are the most common motives, but when the bodies begin to pile up--two suicides, one murder, and the mysterious death of an inmate in one of Scotland's largest prisons--Rebus realizes that there's nothing simple about his latest case. He discovers that beneath the killings a conspiracy is hidden, one that runs all the way to the top of the political ladder.