A young James Mason does a fine job in this film. The story is set a few years before the start of WW II. Mason is a guest at a quiet resort hotel in France. His camera is accidentally used by a German spy who has an identical one. When Mason takes a roll of film to be developed, the roll contains several pictures of top secret French aircraft and facilities. The police question Mason and are able to determine that he is innocent in the matter. But, they use the charges against him as leverage to get him to assist them in finding out which of the other hotel guests is the spy. How he succeeds makes for a most interesting and tension filled story.