Grégoire Ponceludon de Malavoy (Charles Berling) travels to the court of Louis XVI at Versailles seeking support for his plan to drain a marsh in order to relieve his poverty-stricken community from the scourge of malarial fever. Naive in the ways of court, he is robbed and left on the road for dead. A kindly doctor and would-be courtier (Bernard Girardeau) finds Grégoire and nurses him back to health with the help of his beautiful and highly intelligent daughter, Mathilde (Judith Godréche).
Grégoire accompanies the doctor to court where he quickly excels in the fine arts of repartee, ridicule, and sang-froid. Seeing this practice as a route to the king, Grégoire plays the game well and begins to have fun, in spite of himself. He attracts the attention of the influential Comtesse de Blayac (Fanny Ardent) with whom he sleeps, despite his love for Mathilde.
A peasant child's death at home inflames his obsession over the marsh. At the moment he is finally about to have the king's attention, he duels with an officer over a matter of honor; he wins the duel but loses his regal audience for having shot a royal soldier. The film ends in the Revolution: Grégoire and Mathilde are well launched in their drainage project and the doctor is an émigré on the English coast learning the fine arts of British humor.
