Valmont has made an unpleasant discovery. The Présidente de Tourvel has left Madame de Rosemonde's estate without informing him of her intention to leave, or even saying goodbye. In a letter to the Marquise de Merteuil (Letter One Hundred), he rails, ironically enough, against the deceitful ways of women. Valmont spares no time in berating his valet, Azolan, for letting the Présidente slip away. In Letter One Hundred, he orders him to follow Tourvel to her estate and renew his affair with her maidservant to obtain information.

Meanwhile, the Présidente has written to Madame de Rosemonde (Letter One Hundred and Two) to excuse herself and explain, as best she can, her reason for going away. Her reason is, she says, that she is in love. Her guilt and her sense of duty to her husband require her to flee from her beloved, whom she leaves unnamed.

Madame de Rosemonde is both understanding and admiring of Tourvel's choice to flee. In Letter One Hundred and Three she offers the Présidente both her friendship and her protection.

The Marquise de Merteuil is dishing out her own share of advice. In response to Madame Volanges's queries, she writes (Letter One Hundred and Four) that Madame should not rush to grant her daughter's wishes when it comes to marriage. Though she might seek her daughter's opinion on the matter, as a mother, she is best suited to choose her daughter's future husband. A love match, she counsels, will inevitably set Cécile at a disadvantage. The Marquise then writes to Cécile herself (Letter One Hundred and Five), advising her not to be too honest with her mother if she asks her opinion on marriage. Merteuil also writes to Valmont (Letter One Hundred and Six) to mock him for not taking advantage of Tourvel when he had the chance and to inform that she has tired of trying to teach Cécile.

In Letter One Hundred and Seven, Azolan replies to his master. He informs him that he has been doing a little spying at the Présidente de Tourvel's house and that she has been doing nothing but reading and sighing all day.

The Présidente, meanwhile, continues to correspond with Madame de Rosemonde (Letter One Hundred and Eight). In this letter, she reveals the name of her beloved, the Vicomte de Valmont.