After an attempt to rescue a kidnap victim the officer in charge, Supt. Sandra Pullman, who also shot a dog during the raid, is reassigned. DAC Donald Bevan puts her in charge of UCOS, a new unit focusing on unsolved cases. There are no resources available, but Sandra is authorized to hire retired detectives and turns first to her old boss and mentor, Jack Halford, who quickly signs on. Together, they interview a number of ex-policemen and settle on Brian Lane, a reformed alcoholic who retired after a prisoner in his custody died, and Gerry Standing, who seems to know as many criminals as policemen and who won't hesitate to cut corners if it will get him a result. Their first case is that of Roddy Wringer, who is released after 21 years in prison when one of the officers on his case is found to have been corrupt. Bevan is convinced Wringer is guilty and makes it clear that he expects Sandra to prove that. As the investigation progresses, however, it appears that Wringer may not have committed the murder that put him in jail and that the investigating officer knew that but withheld evidence.

The team investigate the murder of a policewoman 17 years ago, but what is Sandra's connection, and what secrets from her days at Hendon are revealed?

Jack Halford hopes a clairvoyant will put him in touch with his late wife. Instead he is contacted by a girl who disappeared twenty years earlier.

A friend of Jack Halford has a diamond that would appear to have been stolen.

The team are on the case of the ice cream bandit, an armed robber whose targets were the ice cream vans of two feuding ice cream manufacturers in the mid 1990s. The battle between the two families erupts into violence, so UCOS decide to track down the bandit and stop the conflict once and for all.