Jacqueline has lost her mind a bit, but whatever, for her trip to the seaside, she has decided to take the train by herself, like a big girl!

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.