The Vicomte de Valmont is determined to seduce the virtuous (and married) Madame de Tourvel, who is living with Valmont's aunt while Monsieur de Tourvel is away for a court case.  At the same time, the Marquise de Merteuil is determined to corrupt the young Cécile de Volanges, whose mother has only recently brought her out of a convent to be married to a former lover of Merteuil.  Cécile falls in love with the Chevalier Danceny (her music tutor) and Merteuil and Valmont pretend to want to help the secret lovers in order to gain their trust, so that they can use them later in their own schemes.

Merteuil suggests that the Vicomte seduce Cécile in order to exact her revenge on Cécile's future husband. Valmont refuses as he wants to devote himself to seducing Madame de Tourvel. Merteuil promises Valmont that if he seduces Madame de Tourvel and provides her with written proof, she will spend the night with him. He expects rapid success, but does not find it as easy as his many other conquests. During the course of his pursuit, he discovers that Cécile's mother has written to Madame de Tourvel about his bad reputation. He avenges himself in seducing Cécile as Merteuil had suggested.

In the meantime, Merteuil takes Danceny as a lover.

By the time Valmont has succeeded in seducing Madame de Tourvel, it is clear he has fallen in love with her.  Jealous, Merteuil tricks him into breaking up with Madame de Tourvel — and reneges on her promise of spending the night with him. In response Valmont reveals that he prompted Danceny to reunite with Cécile, thus abandoning Merteuil.  Merteuil declares war on Valmont, as such she reveals to Danceny that Valmont seduced Cécile.  Danceny and Valmont duel.  Valmont is fatally wounded, but before he dies he is reconciled with Danceny, giving him the letters proving Merteuil's own involvement.  Two of these are sufficient to ruin her health and her reputation, and she flees the country.  Furthermore, her face is left permanently scarred by her illness, and so she loses her greatest asset: her beauty. 

But the innocent still suffer: hearing of Valmont's death, Madame de Tourvel succumbs to a fever, while Cécile returns to the convent.

Confused?  You will be. 

Still, it should be good.  I'll see you there!