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When reporter Walter Garrett finds the dead body of actress Angela Merrova in her hotel room, he immediately phones the police.  By the time the authorities arrive, however, the body is missing, and the next day, the actress appears at Walt's newspaper office and announces that she is suing the paper for printing the story of her death.

Puzzled, Walt visits his friend, Dr. Michael Rhodes, for an explanation, and Rhodes refers the case to his associate, Dr. Francis Flegg, who insists that Walt must have been hallucinating.  Rhodes's interest is piqued when he is called in to identify the body of Rodgers, one of his patients, and Walt insists that the circumstances surrounding Rodgers' murder are identical to those he found at Merrova's apartment.

That night, Rhodes visits Flegg with a blood sample for him to examine, and while he is at the house, he meets Flegg's sinister assistant Marshall Quesne.  On the trail of the story, Walt follows Rhodes to the doctor's house, and when he later sees Merrova enter the building, he convinces Rhodes to visit Merrova with him.

The next day, they both call on the actress at her apartment, where she confirms Walt's story and promises to elaborate the following day.  She mysteriously dies, however, before she can explain.  While digging through some newspaper files, Walt comes across a picture of Quesne that identifies him as Dr. Xavier, a killer executed for murder.  When Walt and Rhodes discover Xavier's empty grave, they confront Flegg, who confesses that he brought Xavier back to life as an experiment, and now Xavier has turned into a monster, killing for the rare blood he needs to remain alive.

After they leave, Xavier appears and shoots Flegg for his blood donor book.  He then kidnaps Joan Vance, a nurse who has the rare blood type he needs, and takes her to his lab.  Walt, Rhodes and the police follow, arriving just in time to shoot Xavier and save Joan from the fate of Merrova and his other victims.