Dr. Marcus Monserrat, Boris Karloff a veteran physician who specializes in medical hypnosis, shares his life with his wife Estelle Monserrat, Catherine Lacey. He has designed a remarkable device that would let him feel another person's experiences and even steer their actions through the power of hypnosis. The concept is groundbreaking but ethically perilous, and the couple grapples with whether such power should ever be unleashed.
They decide any youngster will do as a test subject, and Mike Roscoe is invited to their house with an offer of a new experience. When the device is used, Marcus and Estelle can feel everything Mike feels and can even influence his movements and choices. The test proves successful, and they agree to send Mike away so the experiment can run over a distance.
Mike returns to the club where his girlfriend, Nicole, waits, and he takes her to a local hotel where they share a private moment by the pool. Marcus and Estelle ride along in spirit, experiencing Mike’s sensations as they push the boundaries of their experiment. While Marcus contemplates publishing their work, Estelle grows more excited to chase new thrills and persuades her hesitant husband to keep going with Mike.
The next day, Estelle spots a fur jacket in a shop and convinces Marcus to use Mike to steal it. He reluctantly agrees, insisting this will be a one-time thing. While Mike is at Nicole’s apartment, Estelle and Marcus send him to lift the jacket. Mike departs without telling Nicole, who heads to a nightclub with their friend Alan. Alan confronts Mike, and Estelle drives him to assault Alan and his boss, Ron, Alf Joint.
Estelle relishes the power, while Marcus is shaken by the reckless course they have chosen. When Marcus directly confronts Estelle, she retaliates by assaulting him and destroying the experimental device, effectively ending any chance of reversing the experiment.
Mike lapses into periods where he cannot remember what he’s done whenever Estelle and Marcus control him. A confused Mike visits his friend Audrey, but Estelle makes Mike kill her. He then goes to the nightclub and meets Laura, a pop singer Laura Ladd, and Nicole watches as Mike leads Laura out of the club.
The two are dropped in a deserted street, where Mike guides Laura into a secluded alley and orders her to sing. When she fails to comply, he kills her as a chilling example of the power he wields under Estelle’s influence. The next day, Alan tells Nicole he believes Mike may have killed the girls, and Nicole persuades him to speak with Mike first before taking action.
The police close in, aided by a distressed taxi driver Arnold L. Miller. Alan and Nicole confront Mike about Laura, but Mike cannot recall the events. Under Estelle’s domination, Mike again attacks Alan and escapes in a car. A high-stakes pursuit ensues as investigators close in, with Marcus attempting to intervene and wrest control from Estelle. The car crashes and bursts into flames, and back at the apartment, both Estelle and Marcus die from their burn injuries, ending the chilling chain of experiments and the couple’s dangerous pursuit of power.
