The Metropolitan Police set up a new unit, UCOS, which stands for Unsolved Crime and Open Case Squad, to investigate previously unsolved crimes. Led by Detective Superintendent Sandra Pullman, the team is made up of retired policemen Jack Halford, Brian Lane and Gerry Standing. Their first case is to investigate the murder of a nightclub hostess. The man who was convicted of killing her is released on appeal after serving twenty years in prison, having always claimed his innocence. The renewed investigation eventually produces proof of his innocence, but also his guilt of a different murder. In the end the team finds proof that the man's wife killed the nightclub hostess out of jealousy.