1906. In a crypt-like room, hunchbacked Franz von Holstein mourns over the body of Greta, his young sister and only love. A first flashback shows him sexually assaulting her, after which she expresses her wish to leave this cursed place with him, to live and to be among people. In a second flashback, she teases him into chasing her when she stumbles upon Doctor Herbert von Ravensbrück; they get romantically involved while Franz watches from hiding.
1909. Walter von Ravensbrück (Herbert's son) and his wife Eva are being served tea by butler Simeon when a carriage driving by at high speed is overturned and the coachman fatally impaled. Inside the coach is Greta, unconscious. Inspector Dannick wants to question her, but Walter convinces him otherwise.
Instead, Doctor Sturges is called to check on her. He hears no heartbeat and discovers her gold medallion carrying the inscription "Greta 1906" as well as mysterious symbols, which he recognizes, perturbed.
Getrud, the Ravensbrücks' servant, having recognized Greta, is haunted in her room by Franz von Holstein, who repeatedly vanishes and reappears and cuts her neck open with a scalpel - a wound that bleeds but disappears.
Sturges discovers a scar on Greta's neck on the same spot. He inserts a needle into her right eyeball, causing neither damage nor pain and confirming that Greta is undead. For the coachman's death certificate, he opens the coffin to discover the corpse's rapid decomposition - an indication that he was undead at the time of the crash. Sturges keeps both facts secret.
Gertrud packs her things, leaves, and is chased by Franz's apparition along a path at whose end she is approached by an unseen assailant, who - despite her assertion that she has not told anyone and is leaving for good - murders her.
Meanwhile, Doctor Sturges is working in his underground laboratory. The medallion's symbols contain a formula for the creation of life. Just as Sturges succeeds in bringing one of his corpses to life, he is strangled by an unseen assailant, who also kills the corpse and the doctor's deaf lab assistant.
Walter and Eva both gradually fall in love with Greta. Spying on a love meeting between Walter and Greta, Eva's jealousy escalates. In Walter's absence, she lures Greta into the villa's cellar, where she declares her hate and walls her up alive. She lies to Walter about an unexpected departure of Greta's. Dannick investigates Greta's disappearance, remaining clueless.
A month later, a masquerade ball is held at the villa. In a party game, Eva has to guess the identities of the masked guests. A woman in red whose name she cannot guess puts aside her creepily deformed mask, revealing herself as Greta and vanishing. In disbelief, Eva checks for the body, when the dark cat jumps through the wall opening at her face and runs up the stairs, where Greta appears, smiling. Eva follows her, and Greta's face suddenly turns into that of a rotten corpse. She chases Eva up into the attic, from where she falls to her death, screaming.
Herbert, Walter's father, returns for Eva's funeral. During the ceremony, he catches a glimpse of Greta standing in the distance, which causes him to have a flashback to 1906: Greta dies in childbirth and Franz points his finger at him in accusation.
After Eva's funeral, Herbert stays behind to visit Greta's grave. Greta comes up from behind and reminds him of their baby's prenatal death. When she asks for a kiss, her face again suddenly turns rotten. Herbert, terrified, attempts to escape. He seeks refuge inside a crypt. When the door suddenly shuts tight, Eva's freshly laid corpse slowly gets up and walks towards him.
Walter lies in his bed, falling asleep. The dark cat enters his room, and Walter suddenly notices Greta sitting near his bedside. As she crawls into bed and starts kissing him, her face turns rotten.
In the family granary, Greta lures Simeon out of his hiding place, acknowledging that he did not betray her identity and promising him anything he could wish for: money, or better even, love. She then kills him. As the police are covering up Simeon's body, Walter's body is discovered clutching Greta's medallion.
Inspector Dannick visits Professor Kempte about the medallion's symbols, who explains that the Incans believed they contained a formula which could bring their king back to life. Franz von Holstein, a brilliant former student of his, had worked on deciphering it, but had given up after his sister's death. Kempte gives Dannick Franz's address.
In a final flashback to 1906 and to the room in which the film started, now brightly lit, Franz walks up to Greta, who is dressed in white and holding a bouquet of white flowers. He tells her triumphantly that he brought her back to life and that she is his now, puts the medallion inscribed with the year of her "new creation" around her neck and promises her they will leave and start a new life together. As "proof of love", Greta throws the white flowers at his face. They turn into the dark cat in mid-air, which kills him. Greta, whose dress has magically turned red, giggles and leaves with a smile. Dannick, now entering this room in 1909, discovers Franz's corpse.
At the cemetery, Dannick looks at Greta's photograph on her empty grave, wondering whether he will ever solve the mystery about this woman who he has never even seen. When he returns home, the figure he previously addressed as his wife and which hitherto has been sitting with her back to the viewer turns around. It is an aged Greta smiling at Dannick, who reacts to seeing her, perhaps recognizing her face as Greta's.
The estate's secrets unravel as the repercussions of reanimation and obsession come to a head, leaving lives shattered and the boundary between the living and the dead irrevocably crossed.
The film’s conclusion underscores the dangers of tampering with the natural order—through both forbidden science and uncontrollable passion. By the end, love and vengeance have upended the household, demonstrating that the dead do not rest and the past is never truly buried. The disturbing symmetry between personal and supernatural transgressions delivers a gothic punch.
