(Verbatim from benefactor OddTree)
The Marquise de Merteuil (Glen Close), knowing that Sebastien, Vicomte de Valmont (Malkovich) is starting to fall in love with the virtuous Mme de Tourvel (Michelle Pfeiffer), writes a letter to the Chevalier Danceny (Keanu Reeves). The Chevalier is in love with Cecile Volanges (Uma Thurman), whom Sebastien had seduced and impregnanted; Marquise de Merteuil informs him of this, which incites a challenge from the Chevalier to the Vicomte. By now, the Vicomte has abandoned Mme de Tourvel, saying that he does not love her; he has taken her virtue and tricked her with promises of love and devotion which he negates, even though he really loves her (he thinks he is not good enough, etc., etc.) So the two men fight, and the Vicomte is killed. But before he dies, he takes out blood-soaked envelopes and gives them to the Chevalier; they are letters from the Marquise to him, planning out the seduction of Cecile (because Cecile's mother had wronged the Marquise perviously, something like that) and all the secrets and games.
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Read more about this film at The Internet Movie Database.
Read the source novel, Les Liaisons Dangereuses by Pierre Choderlos de Laclos, on-line here, here or here (if you can read French, that is. I haven't found a freely-available English translation yet)
Buy it on VHS or DVD at Amazon.com.