In 1874, a man’s body, shrouded and forgotten, is buried in a Transylvania grave as an executioner drives a stake through its heart. Immediately afterward, Carl, Victor Maddern, severely physically disabled, steps from the shadows, silences the gravedigger with brutal efficiency, and then summons a drunken doctor to perform a heart transplant on the body before murdering the doctor himself.
Six years heat the chill of that beginning into a deeper nightmare. Dr. John Pierre, [Vincent Ball], is convicted of “malpractice leading to manslaughter” after an emergency blood transfusion—an untested procedure—fails and takes a patient’s life. As John’s fiancée Madeleine watches, he is sentenced to life in a penal colony. Yet fate redirects him to a grim institution, a Prison for the Criminal Insane, run by Dr. Callistratus, [Donald Wolfit]. Here, the doctor intends to use John’s expertise to push forward blood-typing research meant to make transfusions safer, especially for those with a rare and serious blood condition.
At the trial, John defends himself by arguing the death was unavoidable and requests that a professor in Geneva, Prof. Meinster, vouch for him. The judge claims he already sought help, but Meinster replies that he has no knowledge of John. The truth begins to reveal itself when Madeleine and her uncle arrange for Meinster to travel to Transylvania. They meet Auron, a member of the Prison Commission who is secretly on Callistratus’s payroll, and Auron fraudulently fabricates a reply to Meinster’s inquiries, reopening the case in the process.
Inside the murky corridors of power, John grows increasingly uneasy about the source of the blood—many from unwilling inmates who do not survive their donations. Auron returns to Callistratus with word that the Prison Commission has ordered John’s release, a claim Callistratus denies while plotting a different fate for him. He tells John that the commission has denied his appeal and devices a false report that John and another inmate, Kurt, died in an escape attempt. John and Kurt do indeed attempt to flee, but the escape is thwarted; Kurt is likely killed by the vicious Doberman guards that keep the prison under control. Madeleine refuses to accept that John is dead and secretly takes a job as Callistratus’s housekeeper so she can uncover the truth.
John soon learns that Kurt’s grave is empty, a clue that deepens the web of deceit. Auron visits Callistratus again and recognizes Madeleine from their prior encounter. He goes to her room and attempts to assault her, but Carl—having fallen in love with Madeleine—intervenes and stops him. Callistratus demands to know what happened; Madeleine tells him what went down, and Auron denies it, warning Callistratus that he could expose his schemes. In response, Callistratus orders Carl to pursue Auron, and the scientist’s enforcer is sent on a savage chase.
The director of the macabre experiments pulls Madeleine into his laboratory, showing off a disturbing menagerie of “experiments,” including a chained and apparently dead Auron. He binds Madeleine to a wall and plans to siphon Kurt’s blood into her, a stark attempt to save himself by sacrificing another. John, alerted by a distress signal disguised as Madeleine’s handkerchief, arrives and finds her restrained and begins to work a rescue. He is quickly chained himself, and Callistratus orders Carl to strap Madeleine to an operating table, a fate that seems sealed until Carl refuses to comply and is shot.
In a brutal twist, Callistratus reveals his own history: he was executed for vampire-related blood work but had placed himself in suspended animation and was revived through a heart transplant. He now suffers from the same “rare and fatal blood condition” and has drained the blood banks of the prison to keep himself alive. His plan is to transfuse Madeleine’s blood into Kurt, the undead revival needing fresh blood to sustain the operation.
John shouts a desperate plea to Kurt to resist, and the moment becomes a tense struggle as Kurt musters the strength to hold Callistratus’s arm. The struggle brings them within reach of a critical blow, and John finds an opening to knock Callistratus unconscious, freeing himself and Madeleine. The escape is far from over, however; Carl, who survived the earlier gunfire, unleashes the guard dogs before being shot down, and the guards finally end the pursuit. In a final, ferocious denouement, the Dobermans tear Callistratus apart, bringing his reign of terror to a gruesome close.
Throughout this bleak odyssey, the lines between science, obsession, and humanity blur as a man’s ambition to master blood turns into a testament to what people will endure—and do—to survive the nightmare of a world where trust is scarce, and power is wielded with cruel precision.
