An honest expert on locks, Colley Dawson turns safe-cracker after he meets Benny Carfield, unscrupulous dealer in antiques; Dawson steals the goods and Carfield disposes of them, and the resulting profits enable Dawson to lead a double life with small-part film actress Vi. Scotland Yard catches up with him and Dawson is sentenced to ten years in prison. Two years later, in 1940, England is at war with Germany, and the War Office, planning a raid on a German-occupied château in Belgium, is looking for a man who can crack a difficult safe so that the contents, containing lists of Nazi agents in Britain, can be photographed without leaving a trace of the operation. Dawson, in exchange for the eight years of prison awaiting him, agrees to do the job. He, of course, also gets involved with the daughter, Irene, of the local resistance leader.