When one of Regan's snouts complains that his girlfriend's recent suicide was murder, the flying squad detective feels compelled to investigate. He uncovers a conspiracy that reaches the heart of the government, and finds himself fitted up, suspended and under the scrutiny of Special Branch.

The plot is set on a group of bank robbers, who are both violent and successful, strangely getting away each time with an amount around the £60,000 mark, and often leaving behind cash in excess of this sum. The robbers are willing to kill their own team, to get away. As Jack Regan himself puts it after the first raid in the film: "I've never seen so many dead people". Armed with gold-plated Purdey shotguns, they evaded Regan and the Flying Squad for quite some time, before Regan finds encouragement from his Detective Chief Superintendent who was sent down for corruption because Jack wouldn't testify in court for him.

Rough, tough and politically incorrect in the way that only the best 70's dramas can be, Regan was a pilot film for The Sweeney - one of the major television successes of the last fifty years. Featuring John Thaw as the irascible Detective Inspector Regan and Dennis Waterman as his loyal 'oppo' Detective Sergeant Carter, Regan was an immediate critical and ratings hit, resulting in four series of The Sweeney and two successful feature films. Jack Regan is a good copper, but his tough, intuitive style is becoming unfashionable in a Scotland Yard seeking a new image. When a policeman is mysteriously murdered, Regan breaks all the rules to find the killer - but he finds there are men in the Flying Squad prepared to break him.