In Letter Sixty-six, which contains both Letters Sixty-four and Sixty-five, the Vicomte de Valmont writes to the Marquise de Merteuil, first to describe his recent interactions with Danceny with regard to the Cécile affair, and second, to reserve the right to sleep with Cécile if Danceny refuses. Valmont encloses the previous two letters to better document Danceny's behavior. Letter Sixty-four is a draft of a note to Madame Volanges in which Danceny apologizes for having upset her when she discovered his romantic involvement with her daughter. He refuses, however, to stop loving Cécile or to return her letters, as Madame had asked. Valmont notes, in his letter to Mertueil, that no matter how hard he tried, he was unable to convince Danceny to write otherwise. In Letter Sixty-five Danceny writes to Cécile herself. He asks her if she knows who betrayed their secret, swears his undying love, and also mentions that they should use Valmont as their go-between from now on.

Although she had promised never to write him again, the Présidente de Tourvel replies to Valmont's latest entreaty (Letter Sixty-seven). This final reply is meant to prevent Valmont from having any complaint against her. Tourvel offers him friendship and nothing more.

Valmont responds (Letter Sixty-eight) that he cannot simply convert his sublime love for the Présidente into friendship and that to ask him to do so is an insult to his feelings. Cécile, now deprived by her mother of all writing materials, responds to Danceny (Letter Sixty-nine) on a sheet of paper torn from one of his letters. She loves him still, and she is miserable. Also, she does not like Valmont, but she will suffer him, for Danceny's sake.

A new character has arrived on the scene, Valmont recounts. He is Prévan, who announced his intentions to seduce the Marquise de Merteuil at a dinner party Valmont attended. In Letter Seventy, the Vicomte warns Merteuil about this development. He also notes that the Présidente has at long last given in to him. He takes her offer of friendship as an indicator of her willingness to offer more.

In Valmont's next letter (Letter Seventy-one) to Merteuil, he describes his adventures at the Comtesse de B__'s country house, where he only just avoided being caught in a compromising position with her.

Meanwhile, the Chevalier Danceny writes Cécile (Letter Seventy-two) to tell her that he continues to adore her and that she should have more confidence in Valmont. Valmont himself attaches his own note (Letter Seventy-three), announcing that he has arranged for Cécile to have writing materials and that she should turn to him whenever she needs help communicating with Danceny.