The movie depicts the events from July until September of 1914 which led to the defeat of the German troops at the Marne. While Sebastian Haffner explains and comments on operations and decisions on the basis of situation maps, key scenes are depicted by actors. A main focus is thereby placed by Haffner onto the controversial mission of lieutenant-colonel Richard Hentsch who is said to have, during a war patrol to the various army high commands, contributed to the abortion of the operations significantly.

The devil plays the leading role, but rarely has the devil taken such a charming and seductive form as in Anouilh's. As a young girl named Biondetta - blond and innocent as an angel - Lucifer appears to the young Spanish nobleman Alvarez, who is an officer in the service of the King of Naples. In this guise, it is easy for the devil to make the young Spaniard fall in love with him. But Eros has a hard time when strict custom and morality suppress nature. In vain the devil tempts him with the pleasures of the world. Neither carnival, gambling, nor the most beautiful courtesan can yet soften the officer. Or can they?