Dr. Patrick Cory, a dedicated scientist, is conducting research on brain function and potential revival techniques using animal subjects. One night, he is called to the scene of a plane crash and discovers a critically injured man, wealthy industrialist W.H. Donovan. Despite his efforts to save Donovan's life, the man dies. Undeterred, Cory decides to preserve Donovan’s brain in an artificial environment, hoping to study and perhaps revive its functions. As the brain gradually regains consciousness, Cory is astonished to observe that it starts emanating powerful telepathic waves, allowing Donovan to communicate and even exert influence over Cory’s actions.

As the experiment progresses, Cory becomes increasingly obsessive and starts adopting Donovan’s ruthless personality traits. Donovan's brain begins to control Cory's thoughts and actions more aggressively, maneuvering him into carrying out Donovan's unfinished schemes and vindictive plans. Cory’s colleagues and family, especially his devoted wife Janice, become concerned about his erratic behavior and the dangerous ethical implications of his research. The tension escalates as the boundaries between the scientist and the malevolent influence of Donovan’s brain blur, leading to unforeseen consequences that threaten everyone involved.