The scientist Diana Purlow is performing experiments with the mind of criminals sentenced to death in the prison of the sadistic warden Earl Blakely. She tests an apparatus she developed and capable of read minds in a man that claims to be innocent of a murder, but she is not able to convince her former lover and Governor to call off the execution. When the serial killer Jesse Mowatt is arrested and sentenced to death, she convinces the warden to submit Jesse to her experiment. While working with the murderer, Diana faces pure evil in its essence.