D'Artagnan finds the Duke of Buckingham and gives him the Queen's letter. As the Duke is giving the brooch to d'Artagnan, he sees that a piece of it is missing--the piece that Milady, whom he knows as Lady de Winter, cut off the brooch at a ball. The Duke calls a total blockade on all ships leaving English ports, to prevent Lady de Winter from reaching the Cardinal with her portion of the brooch. This blockade represents an act of war against France. The Duke has the brooch repaired, and d'Artagnan races back to France.
D'Artagnan arrives in Paris the night before the ball. He meets with Madame Bonacieux, who takes the brooch from him. The Queen wears the brooch to the ball the following night. The Cardinal can't tell, however, whether the brooch is whole or missing the piece that Milady cut from it--and did manage to get to him, despite Buckingham's blockade. He approaches the Queen and, in front of the King, offers her the missing piece of her brooch. The Queen feigns surprise at the odd gift--the brooch is clearly whole, as Buckingham's jeweler did an excellent job. Later, the Queen summons d'Artagnan to her chambers, secretly allows him to kiss her hand, and gives him a beautiful ring as a token of her gratitude.
At home, d'Artagnan finds a letter waiting for him, inviting him to meet Madame Bonacieux for a tryst the following night. D'Artagnan then visits M. de Treville, who has figured out that d'Artagnan was involved in the odd events between the King, Queen, and Cardinal at the ball, although he doesn't really know how. He begs d'Artagnan to be cautious. He then spots the ring, and d'Artagnan tells him how he "met" the Queen. Treville is impressed, but sees this as even more reason to be careful; in fact, Treville feels d'Artagnan should sell the ring. D'Artagnan refuses, but promises to be cautious. He then goes and meets up with Planchet, and the two head out of the city to the tryst.
At the appointed spot, d'Artagnan sends Planchet off, and waits for Madame Bonacieux alone. After waiting for an hour, he starts to grow anxious, and looks inside the house where they are appointed to meet. There has clearly been a struggle, and she is not there. Mad with worry, d'Artagnan finds out from a local peasant that a group of men, including one smaller than the rest who identified Madame Bonacieux, came and kidnapped d'Artagnan's love.
D'Artagnan heads back to Paris, and tells M. de Treville of his troubles. Treville is convinced that it's a Cardinalist conspiracy, and recommends that d'Artagnan leave Paris to go check on his friends, while Treville will try to find out what he can. Treville's advice is good: when d'Artagnan returns home, Planchet informs him that the head of the Cardinal's guards came around looking for him, under the pretence that the Cardinal wanted to speak to him. After one last check at his friends' homes, during which he picks up a letter from Aramis's house that seems to be from a lady, D'Artagnan and Planchet leave Paris. Before he leaves, d'Artagnan runs into Monsieur Bonacieux, and figures out that he must be the little man who identified Madame Bonacieux to her captors.
D'Artagnan first reaches the inn where he left Porthos to his duel. Porthos is alive, but wounded. D'Artagnan is able to find out some information from the innkeeper: first, Porthos was wounded by a Cardinalist agent looking for d'Artagnan, and second, Porthos's mistress is in fact a middle-aged banker's wife, not a Duchess, as he is wont to claim. The innkeeper knows this because Porthos had to ask her for money to pay for his bill at the inn, which she refused him, thinking that he was cheating on her.
In accordance to that fact that Athos is always melancholy, we actually do know the source. During the book, while Athos and d'Artagnan get drunk, we discover Athos had an ex-wife, which turns out to be Milady. Later, we find that Athos did not know that Milady was a criminal when he fell in love with her. When he learns of her past, he believes that he hangs her.
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