DI Jack Frost investigates a series of commercial robberies. He's assisted by DC Carl Tanner, a black officer recruited by Supt. Mullett to encourage racial balance on the local force. When Frost makes an arrests on the local housing estate, Mullett's only concern is the culprit's racial background as he's concerned that the area not become a racial powder keg. When Frost's informant on the estate is killed, the case becomes a murder investigation, but all of the suspects are black and racial tensions are on the rise. In the course of his investigation, Frost determines that his informant had a number of secrets