Colley Dawson lives a quiet life at home with his mother, but his real life is lived as an expert safecracker at weekends, breaking into wealthy homes and stealing valuable art. When he's eventually arrested and convicted, Colley is approached in prison by Army Major Adbury. He's offered a deal by the Major in exchange for helping with the war effort. Colley will be given his freedom if he uses his safecracking expertise to perform a mission behind enemy lines. The dangerous mission is to break into a difficult safe in a Nazi chateau and steal a list of German spies operating in England. Colley agrees and soon finds himself being trained up as a commando and parachuted into Belgium for the caper of his life.