Valmont has at long last accomplished his mission. Having gained access to the Présidente de Tourvel's house through her priest, he has met and slept with her. He reports this joyous news to the Marquise de Merteuil in Letter One Hundred and Twenty-five, along with the news that Prévan, in addition to being imprisoned, has been forced to leave his regiment following the scandal with Merteuil.

Letter One Hundred and Twenty-six, from Madame de Rosemonde to Tourvel, maintains their relationship as mother and daughter and adds to Rosemonde's list of roles that of doctor. She says that she will care for Tourvel during this difficult time, as she learns to resist her love for Valmont.

In Letter One Hundred and Twenty-seven, the Marquise de Merteuil expresses her disdain for the Vicomte de Valmont's suggestion that they get back together in no uncertain terms. She describes how such a reunion would be disadvantageous to them both, requiring each to make too many sacrifices to the other.

The Présidente de Tourvel confesses to Madame de Rosemonde all that has transpired between her and Valmont (Letter One Hundred and Twenty-eight). She tells her that he now rules her life, and that just as she is entirely devoted to him, so has she entirely accepted her own ruin.

Valmont tries to smooth things over with the Marquise in his next letter (Letter One Hundred and Twenty-nine). He tells her that there is no woman in the world he prefers to her, and that his habit of flattering Tourvel and Cécile in the letters he writes is just his manner of speaking.

Madame de Rosemonde attempts to comfort Tourvel in Letter One Hundred and Thirty by telling her that she is far too good to be loved as fully as she deserves or ever to be happy in love. Rosemonde also speculates on the difference between men and women: women take pleasure from giving love and men from taking.