A rich girl is in love with her father-in-law 's librarian. The wealthy man wants her to marry a military man but she's not prepared to accept it. She rebels and marries the poor guy. This young man has a cousin, who seems secretly in love with him but in fact we 'll never know what she feels. This mysterious sad woman, always dressed in black, gives her relative a strange box which seems to be a bad luck charm. The hand of fate seems on the newlyweds now:the husband involuntarily causes a car crash: his wife is killed.
In an aero-naval base, a marine engineer who was about to deliver the name of a redoubtable spy is murdered. Shortly afterwards three different men appear on the crime scene, each of them claiming to be Monsieur Sylvain, the expected sleuth. But which of the three investigators is actually Sylvain? And what about this delightful young lady who arouses one of the police inspectors? Couldn't she be the murderous spy?
