Dr John Pierre [Vincent Ball] has been convicted of malpractice leading to murder (he attempted to transfuse blood in the 1880s) and has been sentenced to a penal institution for life. Pierre is immediately transferred to a prison for the criminally insane by request of the prison governor, Dr Callistratus [Donald Wolfit].
It's all a setup. Callistratus is doing blood research. Six years earlier, he was called a vampire and sentenced to die and to be impaled in his grave. During his research, however, he isolated a culture which allowed life to remain dormant in his body. After his death, his assistant Carl [Victor Maddern] was able to get Callistratus resurrected. Unfortunately, the culture created an infection in which Callistratus' blood cells are breaking down into a new blood group that is incompatible with any other blood group. He is currently looking for a blood group that will not be antagonistic to these new blood cells. To do so, he is draining prisoners of their blood and performing other hideous procedures in a secret lab, and he wants Dr Pierre's help.
Meanwhile, Madeleine Duval [Barbara Shelley], Pierre's girlfriend, has petitioned the Prison Commission to review Pierre's case on grounds that a letter from Professor Bernhardt Meinster [Henry Vodon] was a forgery. When Callistratus informs the Prison Commission that Pierre was killed trying to escape, Madeleine goes undercover and takes a job as a housekeeper at the prison.
To cut to the quick...Callistratus finds out that Madeleine and Pierre know each other. Callistratus decides to use Madeleine's blood in his latest experiment. Carl, a one-eyed hunchback, has fallen for Madeleine and attempts to save her. Pierre breaks free from his chains. Pierre and Madeleine escape. Carl gets shot. The prison dogs kill Callistratus.
--Original Synopsis by bj_kuehl.