Lady de Winter (Milady), Richelius's spy, has been making life difficult for d'Artagnan. d'Artagnan and his Musketeers chase her, but before they can get to her, she kills Constance to revenge herself on d'Artagnan.

After d'Artagnan and his men capture her, an executioner steps forward and explains that he was the executioner in Lille. He had encountered Milady there; she was a nun who seduced his brother, a priest, and persuaded this holy man to help her steal the valuable communion plate. The priest was later caught for this crime, and the executioner was forced to brand his own brother. Later, in a rage, the executioner managed to track down and catch Milady and brand her as well. Eventually, the priest and Milady escape to Athos's land, but Milady subsequently deserts the priest to marry Athos. The priest commits suicide as a result.

Milady is executed for her crimes, which frees d'Artagnan from his main enemy. The Cardinal gives him a pass that forgives him of any crimes and promotes him to lieutenant.

In a nutshell, the tension in the novel is resolved when Milady is exposed as the criminal she is and executed and d'Artagnan is rewarded by the Cardinal for his cleverness.