Constance comes into the room right after Rochefort leaves. Milady smiles happily, telling Constance that the man who just left played his part admirably.
Milady spins an intricate lie, telling Constance that this man who was really her (Milady’s) brother, who had overpowered the real emissary of the Cardinal.
Milady then explains that the original letter announcing the arrival of D’Artagnan was a forgery, designed to trick Constance.
Milady’s lie works and Constance is overcome with terror. She asks Milady for advice.
Since it will be a race between D’Artagnan and the Cardinal’s emissaries, Milady suggests that Constance leave with her while a servant is posted to ascertain which group arrives first.
Milady proposes that the two of them dine together; Constance goes down to secure permission from the abbess while Milady takes a walk in the garden.
After the women begin their meal, a carriage comes into the convent. Milady tricks Constance into believing that this carriage is from the Cardinal and suggests they leave.
Failing to see that Milady might be pure evil, Constance follows the plan. Before leaving, the two women sit down to eat.
They soon hear hoof beats.
Milady stands up to look out the window. She recognizes D’Artagnan with a sinking feeling, and tells Constance that the Cardinal’s guards have arrived. Constance is so paralyzed with terror that she cannot move, despite Milady’s insistence that she get to the carriage.
Finally, Milady runs over to the dinner table, dumps poison into Constance’s glass, and brings it back for the woman to drink. As soon as Constance drinks the poison, Milady flees, confident that her job at the convent is done.
Constance can hear D’Artagnan’s voice calling to her, and is overjoyed when D’Artagnan bursts into the room and cradles her in his arms.
The two are so happy; Constance begins talking of a certain she, which makes the Musketeers nervous. D’Artagnan implores her to remember the woman’s name, and it soon becomes clear that Milady has successfully poisoned Constance.
Constance dies. D’Artagnan is stricken with grief.
Lord de Winter enters the room, to the surprise of all present. They accept him as one of their own, and the five men pledge vengeance. Although D’Artagnan wants to pursue Milady immediately, Athos cautions patience, saying that certain measures need to be taken.
The others are perplexed about this proposed delay, but Athos wins the debate, and instructs the men to go to sleep.