Valmont (Gerard Philipe) is a wealthy philanderer married to impoverished-but-ambitious aristocrat Juliette (Jeanne Moreau)--a woman with a sterling reputation. They both find this amusing, since she is as faithless to him as he is to her, and they amuse each other with the details of their affairs and the ways in which the use and dispose of their fellow human beings like so much kleenex.
At the moment, Juliette is dallying with a wealthy American named Jerry Court. Not for much longer, mind you; she's searching for a polite way to get rid of him. But at a party she is throwing in an attempt to further her husband's diplomatic career, she discovers that Court has become engaged to Cecile Volnages (Jeanne Valery), a wealthy, virginal young woman. Like most users, she doesn't take well to being on the other end of such things and vows revenge. She asks Valmont to seduce and corrupt Cecile (much, she implies, as he corrupted her). Valmont, who is bored at the moment, agrees. He decides to take his winter ski holiday at the French resort of Majeve where Cecile and her mother (who is a distant cousin of Valmont's) will be spending their Christmas vacation.
While staying at Majeve, Valmont also meets Marianne Tourvel (Annette Stroynberg-Vadim), a kindly young married woman. He regards her virtue as a challenge to his skills as a womanizer, and while searching for a way in which to have his way with Cecile, he also ingratiates himself with Marianne and her mother (Madeline Lambert).
Alas, Cecile hands Valmont the key to her, er, undoing, confessing to him that despite the engagement her parents have arranged, she is in love with a struggling student named Danceny (Jean-Louis Trintignant), who refuses to marry her until he can properly support her. Valmont gets her confession on tape, as well as a message to the young man, and uses it coerce her into sexual relations with him. Having essentially raped the girl, Valmont turns her over to the tender ministrations of his wife, who counsels Cecile to play the field and enjoy the company of all the men who are drawn to her. Back in Paris, she also goes to work on Danceny, encouraging him not to marry Cecile.
Valmont rings up another foul victory when he succeeds in seducing Marianne as well. But this time, things do not go as expected. He falls in love with her. In the end, she proves willing to leave her husband and children to be with him. But although Valmont is initially willing to do the same, he lacks the strength of character she does and when confronted by Juliette, who mocks him for not showing his usual heartlessness, he sends Marianne a telegram ending their affair. Husband and wife essentially declare war on one another.
Matter come to a head at a party where Valmont tries to re-unite Cecile and Danceny. Juliette shows the latter letters proving that Cecile had been seduced by Valmont (not mentioning that the "affair" began with blackmail and rape), which causes the two men to become involved in a violent scuffle, during which Valmont informs Danceny that Cecile is pregnant with his child. Valmont falls during their tangle and strikes his head fatally.
The next morning, when the police come to see her, Juliette is attempting to destroy her correspondence with her husband, knowing that it would expose both of them and destroy the reputation she has so carefully maintained. Unfortunately, she becomes impatient and douses the burning letters with alcohol, which causes the fire to spread to the sleeves of her elaborate negligee. She is severely burned.
Cecile and Danceny exit a courtroom after testifying at the inquest into Valmont's death, shaken but, at least for the moment, a couple. Her mother spots the badly-scarred Juliette in the crowd and remarks that the ugly state of her face reflects the even uglier state of her soul.