The philosopher Denis Diderot, one of the modernists of the French 18th-century Age of Enlightenment movement, is a guest at the château of the Baron d'Holbach. The film depicts the Baron (in reality a major sponsor of Diderot) as a benign host and inventor of amusing machines, including a piganino. Diderot's banned ''Encyclopédie'' is being secretly set up, printed and bound in a crypt beneath the chapel, where the noise of the presses is masked by the playing of an organ.