During World War I, socialite Joel Carter (Rosalind Russell) becomes infatuated with former reporter Bill Gordon (William Powell), who has written a valuable book on cryptology and enlisted in the military. Arranging with her contacts to have Bill stationed to a desk job, Joel ignores her old boyfriend -- who, unbeknownst to her, is a German spy. After Bill discovers that a vital naval code has been broken by the Germans, and that the base is rife with spies, his life and Joel's are threatened.