DS Murphy is working undercover when a member of his "gang" and a mate from school days, Peter Tate, is shot on the street. The dead man's brother, Carl, is out for revenge and the police fear a gang war. Murphy manages to calm them somewhat but Carl is convinced that his brother's is a revenge killing by the Tyler family and sets out to get even. Annie Guthrie eventually joins Murphy undercover in an attempt to get closer to Carl. When Kevin Tyler is killed, the police realize that the only way to stop an all-out war is to identify who really killed Peter Tate and why.