A killer-for-hire gets mixed up with a plot to assassinate England's Prince Phillip.

Colonel Mostyn of British Intelligence is confronted with the task of training a private executioner who can dispose of legally untouchable but dangerous security risks. He recalls Boysie Oakes, who years before had accidentally saved his life in Paris during World War II. Unaware of his mission, Boysie, who loathes violence and becomes ill at the sight of blood, endures the rigorous training program because of the penthouse apartment, expensive wardrobe, a sports car, and female companions supplied by Mostyn. When he does learn the truth, he hires a professional killer to do any dirty work that might come up. He then defies regulations and takes Mostyn's beautiful secretary, Iris, to the French Riviera for a weekend. There he is taken prisoner by counterspies but is permitted to escape because the enemy organization plans to use him as the unwilling dupe in a plot to assassinate the Duke of Edinburgh. Boysie is informed by a courier that during a security check exercise he is to fire blank bullets at the Duke while he is inspecting an R.A.F. base. Real bullets, however, have been placed in his rifle. Although Mostyn arrives in time to prevent the disaster, the identity of the master spy remains unknown. In a moment of unusual recklessness, Boysie leaps aboard a jet bomber as it takes off with the latest anti-missile equipment. Once aboard, he overpowers the master spy, Iris, and somehow manages to bring the hijacked plane back to the base by following instructions radioed to him.