When it becomes obvious that confidential information is leaking out of the Mulberry Street police station, Commander Brian Huxtable and Chief Superintendent John Deakin decide they need the help of a senior officer from that station to find the culprits. They enlist DCI Tony Clark who recently qualified for promotion to Superintendent and is awaiting his transfer. Working with DI Harry Naylor and DS Maureen Connell from the Complaints Investigation Bureau, who are tasked with investigating corruption or misconduct in the police service, they focus on DI Mickey Flynn and DS Paul Tanner. In the end, they set a trap for a senior officer. Clark receives his promotion to Superintendent but finds himself assigned to CIB, which is far from being his first choice.