Milady kidnaps d'Artagnan's friend Constance Bonacieux to lure the musketeer into a death trap.
Constance is marched to a water mill with her hands tied behind her back. Milady's trained monkey Pepe jumps on Constance's shoulders and throws a pink cloth over her face to gag her, but when Constance shrugs Pepe off Milady grabs her and finishes knotting the gag herself.
Inside the mill, Milady ties rope around Constance's waist and hoists her into the air as she sets up an elaborate mechanical booby trap for d'Artagnan. When d'Artagnan arrives, the gagged Constance tries to warn d'Artagnan about the trap, but the cloth over her mouth muffles her cries. The musketeer is unable to understand her and cuts the rope which causes Constance falls to the floor as a trap door opens beneath d'Artagnan, dropping him into a well beneath the mill. Milady appears with a pistol and Constance struggles as she protests in horror through the gag. Milady shuts the sluice gate and the well begins to fill with water as she closes the trap door, sealing d'Artagnan inside.
Milady ties Constance to a support beam and throws a candle into a bed of straw as she leaves, starting a fire. Constance cries out for d'Artagnan through the gag as she struggles as the fire spreads through the mill causing her to cough from the smoke. Inside the well, d'Artagnan uses his last breath to whistle for his preternaturally intelligent horse Rossinante, and he's forced underwater by the trap door as water spills out around it. Constance sees the water and sobs into the gag as she knows that d'Artagnan is drowning.
Rossinante hears the whistle and uses his hooves to kick open the door to the mill. Picking up d'Artagnan's discarded sword in his teeth, he runs to Constance, cutting her free, after which she rescues the musketeer.
