THE STRANGE CASE OF DR. JEKYLL AND MISS OSBOURNE

Fanny Osbourne and her mother arrive at the home of Dr. Henry Jekyll to celebrate their engagement. The party is attended by numerous dignitaries, including General Carew and his daughter; Dr. Lanyon, a close friend and mentor to Henry who is nonetheless nonplussed by Henry's endorsement of "transcendental science"; Enfield, Henry's attorney; and the Reverend. After dinner, the daughter of a guest is found raped and murdered in a bedroom. In the ensuing investigation, General Carew kills the Osbournes' coachman, thinking he is the culprit. Someone finds a broken walking stick that had belonged to Henry; it had been used to beat a young girl to death.
Henry informs Enfield that he has named Edward Hyde as his sole heir should he die unexpectedly. When Enfield protests, Henry assures him that Hyde will take care of Fanny and their mothers. When Henry goes to see if he can revive the coachman, an unknown man appears in the Jekyll household and begins to attack the guests. He ties up General Carew and forces him to watch as he ravishes the general's willing daughter, then beheads another guest when he tries to intervene before trapping a young male guest in the attic and raping him.
Henry returns and professes embarrassment and horror that his guests have been assaulted and murdered. He barricades himself in his laboratory, unaware that Fanny has also hidden herself there. She watches as Henry plunges into a bath of unknown chemicals and transforms into his alter ego: Edward Hyde. Fanny follows Hyde through the house as he brutalizes the other guests, including forcing Mrs. Osbourne to play the piano until her fingers are numb and killing the Carews with arrows. Seeing Fanny, Hyde tells her that he wants to watch her die, then wounds her with an arrow. But before he can kill her or Mrs. Osbourne, Hyde is interrupted by the gun-wielding Lanyon. He takes Lanyard to Henry's laboratory where he plays him a recording in which Henry pleads with Lanyon to give Hyde a dose of a chemical. Lanyard complies and watches in horror as Hyde transforms into Henry. Lanyon dies of a heart attack.
Henry takes the injured Fanny to his laboratory. He explains that he is not a hypocrite: his Jekyll persona is completely sincere in his generosity and humanity, and Hyde is completely sincere in his hatred and refusal to conform to social expectations. Seemingly addicted to Hyde's freedom, Henry prepares another bath. But before he can enter, Fanny immerses herself. She emerges untransformed physically but possessed of the same contempt for morality. She then pushes Henry in, and he transforms into Hyde.
Together, they kill the rest of the guests and servants and destroy the house—including Henry's notes and books on transcendental science. They then escape in a carriage, having violent sex until they transform back into Fanny and Henry.

Fanny Osbourne joins Jekyll in his chemical transformation, and together as altered selves, they slaughter the remaining guests and servants before escaping in a carriage.

The ending unites Jekyll and Fanny in shared amorality, suggesting a rejection of societal constraints in favor of unleashed desire and violence. Borowczyk’s conclusion subverts the traditional duality of good and evil, proposing that liberation from hypocrisy may come at the cost of humanity itself.