Dalziel and Pascoe examine a murder case from 36 years ago for which the wrong person may have been convicted. After 35 years in jail for murder, new evidence shows the police suppressed evidence of bruising on Cissy Kohler the day she was arrested, and she was released. Dalziel had been involved in the 1963 murder investigation, when he was the young assistant to his mentor, Superintendent Wally Tallantire, now in a retirement home. An internal police inquiry is set up to investigate the apparent miscarriage of justice. Dalziel is convinced that the suspect was rightly convicted and enlists an unwilling Pascoe to help him vindicate himself and Wally. Dalziel, however, has kept a possibly crucial piece of evidence in his fridge since 1963 -- the second key to the gun room in which Pamela Westropp was murdered.