At a nightclub in the Catskill Mountains, young magician Corky Withers fails to impress his audience with tired card tricks. At the suggestion of his dying mentor, Merlin, Corky seeks a new avenue of performance and finds success with ventriloquism. Corky and his dummy, Fats, thrive as a team. Corky is taken on by an agent, Ben Greene, who is anxious to introduce his client to a wider market than the comedy club circuit. One night, Ben invites television executive George Todson to see Corky’s show and introduces the two backstage. Several months later, after Corky has made numerous television appearances, Ben meets him for lunch in New York City and informs the ventriloquist that he and Fats might be the stars of a television show. First, Corky must go to Los Angeles, California, and film a pilot episode. Although initially pleased, Corky becomes agitated when he learns that he must undergo a medical examination prior to filming. Despite Ben's reasonable arguments, Corky refuses to see a doctor, claiming that the stipulation offends his principles. In private, Corky engages Fats in conversation, treating the dummy as if it is a real person with a mind of its own. In order to avoid Ben, who believes that Corky is simply afraid of success, Corky takes Fats to the small town where he grew up near the Catskills in Upstate New York. He rents a cabin on Lake Melody at a small resort run by his high school crush, Peggy Ann Snow. Miserable in her unhappy marriage, Peggy is pleased to be reunited with Corky and charmed by his ventriloquist act. Since her husband, Duke, is out of town, Peggy is free to pursue an affair with Corky and the two quickly fall in love. Corky’s relationship with Fats deteriorates as he grows closer to Peggy. During one of Corky's more heated arguments with Fats, Ben appears at the cabin and observes Corky’s precarious mental state. Ben insists that Corky seek help, but Corky promises that he has been regaining his mental health while on vacation. As a test of his sanity, Ben asks Corky to make Fats stop talking for five minutes. However, after two minutes, Corky loses his willpower and picks up the dummy, allowing Fats to deliver a rambling monologue that frightens Ben. The agent gets up to leave and promises to arrange medical help for Corky. As the old man walks back to his car, Corky pursues him and bashes his head, using Fats as a bludgeon. Following Fats’s directions, Corky then dumps Ben’s body in the lake. The next morning, Peggy’s husband Duke returns home and suspects Peggy and Corky of having an affair. Although Duke intimidates Peggy, she lies, insisting that she never slept with Corky. Duke finds Ben’s Rolls Royce abandoned on the property, and Corky explains that the car belongs to his agent, who must have come looking for him. Corky fakes a telephone conversation with Ben, pretending that the agent hitchhiked to a nearby resort. Later, Duke takes Corky fishing and tries to get him to confess to the affair, but Corky lies, convincing Duke of his innocence. When Duke catches something heavy, Corky panics, thinking it might be Ben’s corpse. Duke finally reels in a log, and Corky is relieved until Duke notices Ben’s body washed up on shore. Corky and Duke examine the corpse, but Corky denies that it belongs to Ben. Suspicious, Duke sneaks into Corky’s cabin and finds blood on one of Fats’s wigs, along with Ben’s wallet. Hiding behind a curtain, Corky operates Fats, luring Duke to the dummy, then stabs him to death. Corky informs Fats of his plans to run away with Peggy and leave the dummy behind. Fats responds that Peggy must die because she is coming between them. Instead of killing Peggy, however, Corky chooses to sever his relationship with Fats permanently by killing himself. Excited to run away, Peggy approaches Corky’s cabin, unaware that Corky has committed suicide.