The story takes place in 1788. A mysterious bandit in the guise of a werewolf robs the population and terrifies them. Fabian, a lieutenant in the service of the Austrian hussar army, and his escort are also ambushed. He thereby loses his men and the pay of the garrison. The werewolf has staged the robbery in such a way that Fabian is suspected. The young lieutenant is innocent but is sentenced to the gallows. He manages to escape from prison thanks to Mammelies de Crébillon. This old noblewoman is the heiress to the Ancient Science who bequeathed her a long line of magicians.