Bill and Charlie become involved in the investigation of a petrol station robbery where one of the victims turns out to be the son of a man Bill put away years before. The family believe their father is innocent and that Bill set him up to go to prison seven years ago and accuse Bill of now setting the son up too. Gerry and Vince come to the son's defence and Bill is forced to question the circumstances of the father's arrest, realising his partner at the time was crooked and he is responsible for putting away an innocent man.