Letter I of Dangerous Liasons is remarkably not dangerous. It is taken from the correspondence of two teenage girls: Cécile Volanges to Sophie Carnay. Cécile has just left the convent, where Sophie is still cloistered, to enter the world of society and to get married off.
While Cécile waits for her watchful mother, Madame Volanges, to choose her a husband, back in Paris the Marquise de Merteuil is plotting revenge. Madame Volanges has already selected her daughter's future mate, a certain Comte de Gercourt. As we learn from Letter II, written by Merteuil to the Vicomte de Valmont, Gercourt was once Merteuil's lover. Unfortunately for Merteuil, in a fit of good judgment, Gercourt dumped her for the Intendante, who, incidentally, used to be Valmont's bed-partner. Since their respective break-ups, Merteuil and Valmont have been shacking up. The success of this liaison has led Merteuil to believe they should take revenge on their former partners together. Her plan for revenge is as follows: Valmont should seduce Cécile.
Meanwhile, Cécile is being shown to le monde (society) at her mother's parties, blushing frequently, and falling asleep at card-tables, as she informs Sophie in Letter III. She overhears one gentleman whispering to another, "Il faut laissez mûrir cela," ("That one needs to be left to ripen") in reference to her.
In Letter IV, Valmont accepts Merteuil's suggestion with reluctance. He predicts that Cécile will succumb to his manly charms without putting up much of a fight. A more worthy adversary, he suggests, would be the Présidente de Tourvel, a highly religious gentlewoman whose husband is out of town. It will be a great coup indeed if the notorious Valmont can trick Tourvel into bed.
The cute nuances of Tourvel's conservative clothes and prayer routines are lost on Merteuil. In Letter V, she mocks Valmont for pursuing a nun and warns him that if he does not go to work on Cécile right away, the girl's music teacher, the Chevalier Danceny, will do the job for him.
Valmont responds to Merteuil's insults in Letter VI, with a lengthy catalogue of Tourvel's subtle charms. He notes that her nervous behavior around him may mean that she already has less than pious feelings for him. Perhaps she can be convinced to try to convert Valmont from his wicked ways.