The first episode begins in 1969, at a time when the British police are held to be the most trusted and effective force in the world. But all that is about to change. When a desperate south London villain tips off The Times about how he is being extorted for money by a detective in the Metropolitan Police, something much more shocking is discovered: that at the heart of the Metropolitan CID there exists a 'firm in a firm', a secret network of corrupt coppers. With insider interviews, evocative archive footage and secret recordings, the documentary reveals the story behind The Times's investigation and shows how the public myth of incorruptibility protected the police for so long.