The king wonders briefly why the cardinal is so insistent that the queen wear the diamond tags, but he nevertheless tells the queen about his plans for the ball and instructs her to wear the diamond tags. On further questioning, the queen learns that the idea of having a ball was the cardinal's idea; furthermore, it was the cardinal who suggested that she wear the diamond tags.
After the king leaves, the queen is filled with fear. Suddenly, Constance Bonacieux enters from the closet and reveals that she knows the entire story; furthermore, she promises that she will find someone to go to the duke of Buckingham and retrieve the diamond tags. The queen reminds Constance that a letter would have to accompany the messenger and, if intercepted, she (the queen) would be ruined — divorced and exiled. Constance, not knowing of her own husband's allegiance to the cardinal, swears that her husband will do anything for her. Relieved, the queen gives Constance a jewel to sell in order to defray the expenses of the journey.
At home, Constance discovers that her husband has become an ardent cardinalist and will have nothing to do with her intrigues: "Your queen is a treacherous Spanish woman, and whatever the cardinal does is right," he says. Constance also discovers that her husband is in league with Count de Rochefort, even though he knows that Rochefort is the person who abducted Constance. Monsieur Bonacieux leaves and Constance is certain that he will betray her.
D'Artagnan overhears the entire conversation between husband and wife, and later he is delighted to assert that her husband is a wretch. He then offers himself at her service. When Constance is reluctant to tell d'Artagnan all of the details about the mission, he reminds her that she was about to tell her traitorous husband everything, and furthermore, d'Artagnan loves her more than her husband does.
