The story, however, is what identifies this film as groundbreaking. Catherine Deneuve plays the wife of a successful surgeon with all the bourgeois trappings that comes with her position. But married life does not satisfy her and she has a poor conjugal relationship with her husband. She fantasises extreme sexual encounters both in dreams and by day, with flashbacks suggesting that this is because of being abused as a child and feeling worthless.
She becomes fascinated with les maisons, a euphemism for the Paris brothels. Having obtained the address of one from a friend of her husband, she plucks up the courage to introduce herself to the Madame. It is a high class establishment where she joins two other women. After some initial doubts she soon becomes the one that the men want. Obviously high class and virginal in appearance, with underwear the cost of which could probably feed a family for a month.
The scenes drift between the maison, her incomplete life with her husband and occasional dreamed fetishes, although in one bizarre encounter she actually lives out something approaching one of her dreams.
It all comes down to earth when she becomes too deeply involved with a petty gangster, who for his part wants to own her, the only thing in the way being her husband. He deals with this problem in the way that gangsters do, leaving Belle distraught.
The final scene is one that will cause you to rethink the whole film, and to reanalyse what was real and what was imaginary. I expect it is unlikely that you will succeed completely.
For its time this film was undoubtedly a revelation, both for its theme and the ambiguity it planted in the minds of audiences.