Barnaby's former CID colleague Jack Colby left the force in disgrace following a sex scandal at the Causton police station. Now retrained as a probation officer, Jack is working at a halfway house for reformed criminals. When he is bludgeoned to death, Barnaby sets out to discover why the past would not leave him alone. Guest stars: Chris Barrie (Red Dwarf), Edward Petherbridge (The Borgias), and Christopher Fairbank (Doc Martin, Wolf Hall).