Following "The Two of Us", Claude is now 21 years old. Content with his life, he has a girlfriend Tania and he aspires to become an actor. When he receives his draft notice, a friend convinces Claude he can get out of military service with his connections in Paris. When the connections fall through, Claude is sent for basic training outside Paris before being shipped off to Algeria. His stops in Morocco and Algeria are uneventful as far as military action goes. He returns home with few bad memories of his army life ...

This deftly made French psychological thriller terrifies with its exploration of an experiment gone horribly wrong. Dr. Marc Lacroix, a psychiatrist specializing in brain functions, is obsessed with the link between mind and spirit. To find his link he studies the criminally insane. He builds a secret machine, known only to his mistress Marianne, in which he hopes to exchange minds between humans. He simultaneously wants to help the mentally ill recover, and he wants to experience their madness. He chooses the psychotic killer, Zyto, a man who stabbed at least three women, for his experiment. The initial experiment is successful and the two exchange minds. But trouble ensues when Zyto refuses to reverse the switch. There is little Marc can do when Zyto takes over Marc's life, and more ominously his wife and child whom are unknowingly in mortal danger. Marc, encased in Zyto's body, is returned to the asylum. Will Marc's wife recognize the danger? Will Zyto kill again?

(Claude Berri, who usually participates in films by directing them, here returns to the screen as an over-the-hill lothario, much given to quoting Shakespeare, who occasionally goes around naked under his raincoat and exposes himself to strangers, who are usually not interested in his primitive display of genitalia. It also appears that he is unable to sexually satisfy his much younger lover, and he suspects her of having another boyfriend. He earns his living tutoring students (mostly young girls) in English literature. When, in his frustration, he gropes one of the girls in her home during a tutoring session, she protests, her father (who is at home) beats him up, and he is sentenced to a jail term. There, he is teamed up with a slightly loopy murderer. When he gets out of jail, he finds his girlfriend has left for good, and ends his life.)