For those that don't know Rankin, Rebus is his main character and is an alcoholic Scotish detective with a bit of an attitude problem and an instinctive need to cross any line he comes across (which, when I up it like that, makes him sound a lot like other modern detective thriller characters, which he is I guess). While the main crux of Rankin's stories are the mysteries, he uses it to have a dig at politicians, the establishment and the grind of every day life there.
In this book he's investigating the death of three rapists who seem to have been killed by the same person and the seeming accident (or suicide) of a local MP. When you look at the mystery itself, it boils down to a reheating of an old Agatha Christie/Hercule Poirot mystery from a few years ago (I won't tell you which one because I can't remember the title and it'd give the story away). It's still a good book though because of the grainy grind that goes along with the story though.