The only son of wealthy widow Violet Venable dies while on vacation with his cousin Catherine. What the girl saw was so horrible that she went insane; now Mrs. Venable wants Catherine lobotomized to cover up the truth.

A scientist takes a the brain of dead man and revives it via electrodes as it lays suspended in a tank of liquid. Soon, the brain grows to possess enormous psychic powers and inflicts its personality upon the doctor who saved creating a "Jekyll and Hyde" paradigm.