Aged Marcus Monserrat, a discredited medical hypnotist, argues with a newsagent about the placement of a shop-window advertisement for his services. After resolving the dispute, he returns home to his wife Estelle. They eat a meal while they discuss the imminent testing of a hypnotism machine that Marcus has invented.

Later, at a nightclub, bored young man Mike chats with his girlfriend, Nicole and his friend, Alan. Mike insists that they leave the club. Afterwards, he deserts his two companions and wanders off alone.

Meanwhile, Marcus and Estelle decide that the hypnotism machine should be tested on a stranger in search of new experiences. Marcus takes to the streets to find a subject, and meets Mike in a Wimpy Bar. Mike, intrigued by the old man, returns to Marcus's home, and undergoes hypnosis induced by the apparatus. Unwittingly, Mike puts himself under the mental control of Marcus and Estelle: he is now responsive to their mental commands, even when far away, and, by concentrating, they are able to vicariously experience all his feelings and sensations.

Using their new power, Marcus and Estelle compel Mike to go swimming. He does this, sneaking into a private pool with Nicole. Marcus and Estelle share his experience. Finally certain that the hypnotic technique works, Marcus is keen to use it to help other old people. Estelle, however, wants to keep the technique a secret and use it purely for personal gratification. Marcus agrees to keep the technique secret for a little while.

The following day, Estelle decides that she will use the power to make Mike steal a fur for her. Marcus, though unhappy with her behaviour, agrees that she may do this. Later, Mike calls on Nicole, with whom he has a date, but, using her hypnotic power, Estelle compels Mike to leave while Nicole dresses. Mike breaks into a furrier's shop and steals a fur. Estelle and Marcus find that they are excited by the theft. Mike, confused and bewildered, returns to Nicole's house. He does not mention his crime. She is angry that he left without telling her, but they end up sleeping together.

The next day, Estelle decides that she wants to experience the thrill of speed. She compels Mike to steal Alan's motorbike. With Nicole riding pillion, Mike speeds out into the countryside. Eventually, Mike returns the bike. Alan is angry. Estelle compels Mike to fight Alan. Estelle enjoys the experience; Marcus is disgusted. Estelle realises that her power to control Mike seems stronger than that of Marcus. Marcus decides he will bring the boy back to release him from their control, but Estelle trips him up and, while he lies on the floor, smashes the hypnotism machine, before tying Marcus to the sideboard.

Meanwhile, Alan and Nicole discuss Mike's strange behaviour. She tells Alan that she no longer cares for Mike. Elsewhere Mike, ever more confused, visits an old flame. Estelle compels him to murder her with a pair of scissors. Afterwards, Mike goes to the nightclub, where he is spotted by Nicole and Alan. Shortly afterwards, Mike leaves the club in a taxi with a singer; under Estelle's control he later strangles her.

The next day, Alan and Nicole search for Mike, while a taxi driver reveals to a colleague that he saw Mike and the murder victim in his cab the previous night. The police begin to search for Mike. Nicole and Alan find Mike in the antique shop where he is employed. Estelle attempts to compel Mike to kill Alan. The two men fight; Mike flees in a car. The police arrive and chase after him. Marcus makes a final effort to overcome Estelle's will. He manages to take control of Mike and under his influence the young man crashes the car he's driving. The vehicle bursts into flames; trapped inside, Mike dies. Marcus and Estelle, sharing his experience, die too; their charred bodies are all that remain.