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.
Danceny replies (Letter One Hundred and Fifty-seven) gallantly to say that he will fly to his Cécile's side.
Valmont then composes another missive to Merteuil (Letter One Hundred and Fifty- eight), in which he mocks her for getting stood up by Danceny. Merteuil sends Valmont a court note in reply (Letter One Hundred and Fifty-nine), stating her annoyance with such cheap tricks.
Again, Madame Volanges writes Rosemonde (Letter One Hundred and Sixty) this time to send along a mysterious letter Tourvel dictated to her maid. The Présidente lost consciousness before the envelope could be addressed, but one can guess for whom the letter is intended. The letter itself (Letter One Hundred and Sixty-one) is addressed at first to a cruel and malignant man, but moves on to direct itself toward a wronged husband, and then returns to the evil lover again.
It seems that Merteuil has been active on the warfront. Danceny writes to Valmont (Letter One Hundred and Sixty-two) to summon him to a duel for the wrongs he has committed. The next letter (Letter One Hundred and Sixty-three) is proof that Danceny has carried out his duty: it is a report to Madame de Rosemonde that Valmont is dead, run through on Danceny's sword. Before he died, however, Valmont managed to hand over a collection of papers, which one can only assume are his damning letters from Merteuil. Letter One Hundred and Sixty-four is a request from Madame de Rosemonde that Danceny be prosecuted for her nephew's murder.
Finally, the word "danger" is put down on paper. In Letter One Hundred and Fifty, Danceny writes to the Marquise de Merteuil, We are to deny ourselves a correspondence which, according to you, is dangerous and for which there is no necessity (...et nous nous priverons d'un commerce qui, selon toi, est dangereux, et dont nous n'avons pas besoin).
Either a theme of danger has finally been introduced to the novel, or it has only now surfaced even though it was present all along. However, Danceny's change of heart seems more dangerous than his actions. As readers, we feel endangered by Danceny's changeableness. Was he not a moment ago the one character in the novel whose feelings and intentions were devoted to a single other person alone? Was he not truly and unswervingly in love with Cécile?
An even more extreme and realistic danger is the Marquise de Merteuil's simple declaration of war with Valmont. In a word, she brings about the collapse of the complex formation of deceits and liaisons she and Valmont shared with each other. A single, lonely, and undelivered letter lingers in the no man's land between the Présidente de Tourvel's sickbed and the world. This missive is condemned to spend the rest of eternity in a place of anticipation, not unlike the purgatory the Présidente's soul will soon inhabit.