As Christmas Eve approaches, Drusilla’s excitement over her new gown highlights the fact that Winifred only owns a plain black dress. Mrs. Pounds summons Winifred to her chambers and offers her a vivid, apple-green dress. While waiting for the dress to be fetched, Winifred notices framed daguerreotypes of Mrs. Pounds’ deceased children. Mrs. Pounds speaks of them and of the first Mrs. Pounds, who allegedly developed dark bruises on her neck before her death. 

Winifred humbly accepts the dress but, leaving the room, overhears the lady’s maid Amelia ask whether the dress was colored with the same arsenic-based dye that recently killed a local woman. Winifred hides the dress in her wardrobe, where its folds make it look like a woman trying to claw her way out. That night, she enters the bedroom of the guest Marigold and her husband; they wake and sense a presence, scanning the room with suspicion, but never quite manage to meet her eyes.

At the Christmas Eve celebration, Winifred wears the green dress. She pins her mother’s pearl brooch above her heart before leaving her room, then swallows it upon seeing the footmen’s solemn faces in the hallway. 

During the gluttonous feast, she observes the guests’ crude behavior and watches as the footmen spit into the food before serving it. Afterward, while the guests dance, Winifred steals Marigold’s smelling salts and wanders the empty upstairs halls, at one point entering a hidden attic garret filled with corpses. She then finds the servants telling ghost stories; she tells the William Batt ghost story before confessing she fears she is herself a ghost, to which the butler replies that they do not like her very much. 

Returning to the party, Winifred joins a game of blind man’s buff. She catches Drusilla and discovers a painting knife hidden up her sleeve. Winifred then has a vivid, violent hallucination of stabbing Drusilla repeatedly, though the narrative immediately confirms this was only a fantasy and Drusilla is unharmed.

On Christmas morning, Winifred follows Mr. Pounds to the library and reveals that she is his illegitimate daughter, presenting the eyes she cut from the family portraits as proof of their shared ancestry. Mr. Pounds furiously rejects her and terminates her employment. 

Immediately after, Winifred retrieves a cleaver and begins a massacre. She starts by cutting off Miss Manners’ hand at the piano, then kills Mrs. Manners with a brooch pin and Mr. Fancey first by striking him with a poker he had seized himself, then strangling him with a bootlace pulled from his own shoe. After murdering the Dowager, Art Fishal, and Marigold’s husband, she moves to the kitchen and kills several servants, force-feeding some with salt of sorrel. Taking a crossbow from the armory, she goes to the nursery, where Mr. Pounds shoves his wife and son toward her before fleeing. Winifred shoots mother and son with bolts. The nurse, after Winifred shouts after her to go free, glances back as she runs, trips, and falls over the banister to her death. 

After killing Mrs. Fancey and Mrs. Able, Winifred finds Mr. Pounds in the dining room, his ankle caught in the leghold trap she had set earlier. In an attempt to placate Winifred and get her to spare his life, Mr. Pounds disowns Drusilla as his daughter. After he insults her, she fires a bolt she intends for his heart, but approaching the collapsed body discovers the shaft protruding from his shoulder instead. Mr. Pounds lunges at her with a carving knife, but Drusilla appears with a rapier and fatally stabs him through the heart.

With Drusilla now working as Winifred’s accomplice, the final killings conclude: Winifred shoots the butler from his perch on the chandelier, kills a fleeing red-haired servant, and shoots the gardener in the gardens, while Drusilla slashes the gamekeeper’s neck and stabs Marigold in the neck in the Great Hall. 

For the next 11 days, the two sisters live in the house among the dead, arranging the corpses at the dining room table and letting the horses roam inside. During this time, a scullery maid who had been hiding in the secret garret among the corpses escapes, and a woman from a neighboring farm peers through a window, sees the carnage, and flees in horror. 

On the 12th day, the police arrive to find bodies hanging from the trees. Drusilla stages a scene, tying her own wrists and claiming to be a survivor of the massacre. She tells the authorities that Winifred alone was responsible for all the killings. Believing her story, the police arrest Winifred and take her away.

Winifred is led to the gallows for a public execution, laughing as she faces a cheering crowd of 30,000 people. She spots Drusilla among the spectators. When the chaplain asks if she has anything to say regarding her guilt, Winifred replies, “It was grand” (190). She refuses to wear the traditional hood, wanting to see the crowd as she dies. The executioner, who favors the short-drop method of slow strangulation, removes the bolt and the drop falls, and as she is hanged, Winifred’s mind fills with memories of her past acts of cruelty. 

Winifred notes that her sensational story will be sold in penny dreadfuls and that a cast of her head will be made for phrenological study.