In 1917 Lt. Bill Gordon is headed for France when he meets and becomes friendly with Joel Carter, niece of the Asst. Secretary of War. Finding out that he is an expert on codes, she gets her uncle to cancel Bill's orders and has him reassigned to break enemy codes. In his new assignment he becomes involved with beautiful Russian spy Olivia Karloff, who is working for the Germans, and must juggle Joel's affection and his pursuit of Karloff's connections to retrieve a stolen code book.