The Hellbound Heart recap

Frank Cotton opens an intricate puzzle box seeking sensations beyond ordinary life and is taken by the Cenobites, beings for whom pain and pleasure have merged. Later his brother Rory and Rory's wife Julia move into the house where he vanished. Blood from an accident partly restores Frank beneath the attic floor, and Julia, still obsessed with him after an earlier affair, murders strangers so he can rebuild his body from theirs. Rory's friend Kirsty uncovers the secret, escapes with the box, and accidentally calls the Cenobites. She bargains for her safety by promising them Frank. Frank kills Rory and wears his skin, but Kirsty exposes him and the Cenobites reclaim him. Julia also dies, and Kirsty survives with the closed box and the disturbing knowledge of the world it can open.

Frank Cotton has pursued increasingly extreme pleasures across the world. Convinced that an ornate puzzle box can open a path to experiences unavailable to ordinary people, he prepares an empty room and solves the mechanism. The opening summons the Cenobites, altered beings whose understanding of sensation has erased any useful boundary between pleasure and agony. Frank realizes too late that their promises meant something very different from what he imagined. They take him out of the human world, leaving the room bare and the box closed. Some time later, Frank's brother Rory and Rory's wife Julia take possession of the neglected family house and begin making it habitable. Julia approaches the move with little enthusiasm, while the building retains the concealed aftermath of Frank's bargain.

Rory and Julia continue restoring the house, helped by Rory's friend Kirsty, who suppresses her romantic feelings for him. The move also revives Julia's memories of a brief, intense affair with Frank shortly before her marriage. While working, Rory cuts his hand and bleeds heavily in the room where Frank vanished. The blood reaches what remains of Frank beneath the floor and gives him enough substance to return as a fragile, unfinished body. Julia discovers him in hiding. Frank tells her that human blood can restore him and appeals to the desire she still feels for him. Rather than expose him, she accepts his presence and begins considering how to obtain what he needs without Rory learning that his brother has returned.

Julia begins approaching solitary men away from the house and bringing them back under the pretense of sex. She kills them in the upstairs room, allowing Frank to consume their blood and tissues. Each victim makes his body more complete, while Julia grows more practiced at concealing the murders from Rory. Frank remains afraid that the Cenobites will discover his escape and insists that he must become whole quickly. Rory senses that his wife is withdrawing but does not understand why. Kirsty, already uneasy about Julia and protective of Rory, notices the pattern of secrecy. Her concern draws her toward the house and the locked room where Julia has been feeding Frank.

Kirsty follows Julia and discovers the nearly restored Frank. He attacks her, but she escapes with the puzzle box and collapses outside. Taken to a hospital, she solves the box while trying to understand it and summons a Cenobite. Faced with being taken herself, Kirsty explains that Frank escaped the beings after accepting their summons. She bargains for her freedom by offering to lead them to him. The Cenobite accepts the exchange if she can prove the fugitive's identity. Kirsty returns to the Cotton house knowing that Rory is in immediate danger and that Frank may now look sufficiently human to hide in plain sight. Meanwhile, Frank and Julia prepare to complete his restoration, with Rory the closest available victim.

Frank kills Rory and covers his restored body with his brother's skin, presenting himself to Kirsty as the injured man she hoped to save. His behavior and knowledge expose the disguise. Kirsty forces the truth into the open and calls Frank by name, giving the waiting Cenobites the proof required by her bargain. Julia dies amid the violence of the confrontation. Frank tries to escape responsibility for his original summons, but the Cenobites bind and reclaim him, carrying him back into their realm. Kirsty survives as the sole remaining member of the group, while Rory, Julia, and Frank are dead or lost beyond the human world. The puzzle box returns to its closed state. Looking into it, Kirsty senses Frank and Julia but not Rory and wonders whether some other hidden mechanism might open a way to paradise rather than the Cenobites' domain.

Frank kills Rory and uses his brother's skin as a disguise, hoping to escape before the Cenobites find him. Kirsty recognizes the deception and names Frank to the beings she summoned. Julia dies during the confrontation, and the Cenobites reclaim Frank, tearing him out of the human world despite his attempts to deny his identity. Rory, Julia, and Frank are all gone, leaving Kirsty as the only survivor of the household. The puzzle box closes and returns to its apparently harmless form. In its polished surfaces Kirsty perceives traces of Frank and Julia but not Rory, and she wonders whether another device might open a passage to a gentler afterlife. She is left with the knowledge that hidden doors exist and that desire can make their terrible costs seem invisible until too late.