The Chevalier Danceny writes to the Marquise de Merteuil (Letter One Hundred and Fifty) to gush about the bliss he anticipates at their reunion.
Valmont is not insensible to the Marquise's sudden preference for Danceny. He writes to her (Letter One Hundred and Fifty-one) to protest being treated like a schoolboy. He threatens that unless she starts acting toward him as he would like, he will be forced to take revenge on her.
The Marquise replies (Letter One Hundred and Fifty-two) that will not let any man control her. She tells Valmont that, first of all, he has no proof that Danceny has become her lover, and second of all, he can go ahead and bring the vengeance, for all she cares.
Valmont offers the Marquise an ultimatum (Letter One Hundred and Fifty-three): either they join forces, or they go to war. The Marquise's response, on the same piece of paper is "War."
Meanwhile, the Présidente de Tourvel is wasting away. Madame de Volanges writes to Madame de Rosemonde (Letter One Hundred and Fifty-Four) to bemoan their friend's impending death.
Valmont decides to start the war right away. He composes a letter to the Chevalier Danceny (Letter One Hundred and Fifty-five) in which he reminds Danceny of his infidelity to Cécile. He suggests that Danceny stand that old Marquise up and go see Cécile instead. Indeed, to this letter, Valmont has attached a letter from Cécile (Letter One Hundred and Fifty- six) begging Danceny to come and visit her.