The visitor is Count de Rochefort, the cardinal's right-hand man, the person whom d'Artagnan always refers to as "the man from Meung." Milady immediately tells him three important matters: (1) Buckingham is either dead or seriously wounded; (2) she has become a close confidante to Constance Bonacieux, whom the cardinal is searching for; and (3) the four musketeers will be arriving soon. The count is to report immediately to the cardinal, but Milady asks that he leave his chaise, his servant, and his money at her disposal. He is also to instruct the Abbess that Milady is to be allowed to walk in the woods.
Milady then plans her revenge. She pretends that the visitor was her brother, and she convinces Constance Bonacieux that the letter from Madame de Chevreuse is a forgery and that they must flee to a secret cottage that Milady knows about. Suddenly they hear hoofbeats and, leaving Constance seated, Milady peers through the window and sees the musketeers approaching. She tells Constance that it is the cardinal's men and they must escape through the woods. Constance is so paralyzed with fear that she can't move, so Milady pours her a glass of wine, while opening a secret ring and pouring poison into the wine. Then she makes the innocent and trusting Constance drink the wine. Afterward, she flees for her life.
D'Artagnan and the others arrive and find Constance weak and dying. With her last bit of strength, Constance embraces d'Artagnan and tells him that she loves him. As he holds her tenderly in his arms, she is able to remember the name of the woman who gave her the poison. Then she dies, and d'Artagnan "now held only a corpse in his arms." At this moment, de Winter enters, identifies himself and explains that he has been following close behind Milady ever since the death of Buckingham.
D'Artagnan is prostrate with grief, but is comforted by Athos, who tells him to "weep, weep, young heart filled with love, youth, and life!" The other musketeers want to take revenge against Milady immediately, but Athos insists that he be in charge because "she is my wife."
