 Marc Lacroix is a psychiatrist, a student of the brain, with a rocky marriage, a mistress, and a ten-year-old son. He also has a secret laboratory where he s built a machine he thinks will allow him to penetrate the mind of any person hooked up to the machine with him. He tests it with Zyto, a psychopath who has killed three women. The machine fails and exchanges the men s brains. Zyto passes himself off as Marc, and Marc (now in Zyto s body) escapes from the asylum to the flat of his mistress. She tries to warn Marc s wife, exposing herself to Zyto. All are now in grave danger. Can Lacroix find a way to get Zyto back to the machine before irreversible damage is done?