The term "mousetrap" is explained as being a method whereby the police trap friends and/or associates of a person who has been arrested for political reasons. Here, the authorities have placed four guards at Monsieur Bonacieux's house, and they plan to arrest anyone who knocks. Meanwhile, upstairs, d'Artagnan has removed most of the first section of the flooring in his apartment so that he can hear the entire proceedings. When he hears the guards manhandling Constance Bonacieux, he sends his servant, Planchet, to enlist the aid of the three musketeers, and grabbing his sword, he flies to Constance's rescue. Only one of the guards is armed, and after a short time, d'Artagnan is able to drive all four men from the premises in a manner so dashing and thrilling that Constance is marvelously impressed and eternally grateful.
Constance Bonacieux turns out to be young (in her early twenties), charming, and beautiful. When she describes the man who abducted her, d'Artagnan recognizes him as "the man from Meung." She tells d'Artagnan about her escape: she was left alone, so she immediately tied some sheets together and let herself down from a window. She feels so deeply grateful to d'Artagnan that she entrusts him with a secret password which will gain him entrance into the palace to see Monsieur de La Porte, whom he is to send to her. When d'Artagnan delivers the message to La Porte, the gentleman advises him to find someone whose clock is slow and go there and establish an alibi.
Afterward, d'Artagnan daydreams about a romantic love affair with Constance Bonacieux, and while wandering idly through the Paris streets, he finds himself outside Aramis's house, where he sees a lady in a cloak knocking at what appears to be Aramis's window. He sees the woman talking to another woman, and when she leaves, he discovers that it is Constance Bonacieux. He follows her and accosts her. She denies knowing Aramis, and when she refuses to reveal the secret of her mission, d'Artagnan offers to escort her to her destination. She permits him to do so on condition that he leave and not follow her. D'Artagnan promises and returns home, where he learns that Athos has been arrested by authorities who thought that they were arresting d'Artagnan.
