The philosopher Denis Diderot, one of the modernists of the French 18th century Age of Enlightenment movement, is a guest at the rural castle of the Baron d'Holbach, and prints in hiding in the chapel his forbidden Encyclopédie, drowning the noise of the presses in Jewish assistant Abraham's organ playing.
Then arrives from Berlin, Madame Therbouche, a flirtatious painter and intrigante?. She has made a painting of Diderot's idol, fellow-philosopher Voltaire, and convinces him to be more daring and to pose for her in the nude, leading to an animated row with his wife Antoinette. The scene is witnessed by a feared visitor, Baron d'Holbach's brother, the Cardinal, who is hunting for the illegal Encyclopédie printers. To divert him, the Baroness confesses to him her real and imagined sins and next send every female of the castle to do the same, notably her guest the depraved Madame de Jerfeuil, who is having a lesbian affair with her cousin, later joined spontaneously by her husband the Chevalier de Jerfeuil, who had just been seduced by two male guests of the Baron, the Marquis de Cambrol and the Marquis de Lutz.
Through it all, Diderot's ideas keep changing about the article he is working on, morality. Eventually secrets end up getting out, both the painter's true agenda (she is a thief) and what is going on in the chapel, while the Cardinal "recollects" himself after hearing so many lustful sins.