Saints of the Shadow Bible (Inspector Rebus #19) by Ian Rankin

Rebus is back on the force, albeit with a demotion and a chip on his shoulder. He is investigating a car accident when news arrives that a case from 30 years ago is being reopened. Rebus's team from those days is suspected of helping a murderer escape justice to further their own ends.

Malcolm Fox, in what will be his last case as an internal affairs cop, is tasked with finding out the truth. Past and present are about to collide in shocking and murderous fashion. What does Rebus have to hide? And whose side is he really on?