The Vampire

In San Francisco, Dr. Campbell has begun experimenting with vampire bat blood just before his death. After Campbell's passing, his colleague Paul Beecher discovers a bottle of pills among his effects, hinting at the controversial research behind the blood work.

Betsy Beecher, the doctor’s daughter, accidentally substitutes the vampire-blood pills for her father's migraine tablets. The switch sets off the chain of events that will affect Paul and the course of the investigation.

Driven by the pills, Paul begins experiencing blackouts that disrupt his medical work and judgment. The episodes foreshadow more dangerous consequences linked to Campbell’s experiments.

During a consultation with Marion Wilkins, who suffers from congenital heart problems, Paul feels unwell and asks her to return the next day. The following morning, Marion grows gravely ill and dies, with two puncture wounds found on her neck.

Paul returns to Campbell's lab and encounters Dr. Will Beaumont, the head of the university’s psychiatric department, accompanied by Henry Winston. Beaumont explains that Campbell's work involved regressing minds to a primitive state and reversing the process to advance intellect.

The next morning, Henry Winston is mysteriously found dead, showing puncture wounds on the neck and tissue disintegration. Paul is unsettled by the deaths and the pattern he’s involved in.

Paul is called to perform an emergency surgery but cannot focus due to the lingering effects of the pills, forcing him to leave the operating room. The incident underscores the growing danger of his condition.

Realizing the murders may be his own doing, Paul arranges for Betsy to stay with an aunt for safety. He confronts Dr. Beaumont’s associate Will, who locks the pill bottle in a drawer to prevent access.

During the night, Paul transforms into a vampire and murders Will, disposing of his body in a furnace. The crime intensifies the mystery around the pills and Paul's own humanity.

Sheriff Buck Donnelly visits the lab and, suspecting Will’s experiments, discovers an audio recorder containing a recording of Will’s murder. The recording confirms foul play and implicates Paul.

Nurse Carol Butler visits Paul's office and notices a vial of poison. She realizes Paul may intend suicide and witnesses his transformation into a vampire before escaping.

Carol flees into a nearby wood with Paul in pursuit, and Buck Donnelly follows, preparing to intervene as the danger escalates.

Officer Ryan arrives and shoots Paul, who falls into a shallow culvert. As he dies, his monstrous body reverts to his ordinary appearance, ending the threat.