Just before Dr Matthew Campbell [Wood Romoff] dies, he passes on the product of his
long years of animal research to Dr Paul Beecher [John Beal] . "It's the pills," he
whispers. When Beecher gets a migraine, his daughter Betsy [Lydia Reed] mistakenly
gives him one of the pills. That night, Beecher sleeps soundly but Marion
Wilkins [Ann Staunton] is bitten by a vampire. When she is examined the next morning by
Beecher, she gets hysterical and has a heart attack.
Dr Will Beaumont [Dabs Greer] comes from the university to investigate Campbell's work. He knows only that it involved base instincts and some sort of addicting pills that change the brain chemistry after only one dose. The pills must then be taken every 24 hours or the 'animal' goes crazy. More people begin to die. They all have two puncture wounds on their throats and appear to have died from 'capillary destruction'. Sheriff Buck Donally [Kenneth Tobey] gets suspicious and exhumes the bodies only to find them in a severe state of 'cellular destruction'. Some virus, apparently introduced by the neck wounds, is eating their tissue.
Beecher suspects himself. He asks nurse Carol Butler [Coleen Gray] to keep him company one night but gets called away to surgery. At 11pm, he transforms into an ugly caricature of himself. He follows Carol home but she gets away. The next night he stays with Beaumont but, when Beaumont takes away the pills, Beecher goes crazy and kills him. The next morning, Beecher decides to kill himself. Carol shows up early for work and tries to stop him. When they fight, Beecher transforms. He pursues Carol into the forest; Donally pursues them both. Beecher is shot 3 times by the deputy as he struggles with Donally. [Original synopsis by bj_kuehl]