In 18th-century Rome, impish aristocrat Onofrio del Grillo amuses himself by playing pranks on all sorts of people — his reactionary family and fellow nobles, the poors, the French occupiers trying to modernize society, and even the Pope himself.
A playwright offers two actress friends the chance to appear in his new, unfinished play, which consists of only one female part.
Joa (Bulle Ogier), an archaeologist from Mexico, comes to Paris in search of her sister Anna (Mireille Perrier), of whom she is suddenly without news. Anna, a theater actress, was in the title role in Sade's "Justine" when she disappeared. The investigation leading Joa to the people who have known her sister, turns into an initiatory quest. Her journey, her stroll through a subterranean marginal Paris, leads also to the emergence of a new woman.
