Magic

After Charles "Corky" Withers (Hopkins) fails in his first attempt at professional magic, his mentor Merlin (E.J. André) says that he needs to have a better gimmick. A year later, Corky comes back as a combination magician and ventriloquist with a foul-mouthed dummy named Fats, becoming a huge success. Corky's powerful agent, Ben Greene (Meredith), is on the verge of signing him for his own television show, but Corky bails out for the Catskills, where he grew up. His talent agent thinks that Corky is "afraid of success." In truth, Corky does not want to take the TV network's required medical examination because the doctors might find out that he suffers from severe mental issues, and that even off-stage he cannot control Fats (a manifestation of Corky's id).

In the Catskills, Corky reunites with his high school crush, Peggy Ann Snow (Ann-Margret), who is stuck in a passionless marriage with Duke (Ed Lauter), Corky's friend from high school. A magic trick with a deck of cards charms Peggy into thinking they are soulmates, leading to them having sex. This sparks the jealousy not only of Duke, but also the dummy Fats. In the midst of an argument "between" Corky and Fats, Greene arrives unexpectedly and confronts Corky, discovering the truth about Corky's state of mind. Corky pleads that nothing is wrong with him and that he is just rehearsing, so Greene puts him to the test, saying "Make Fats shut up for 5 minutes." Corky puts aside Fats, but is unable to last 5 minutes without delivering a rapid stream of speech through Fats. Greene demands that Corky get help and leaves to make some calls to the doctors, but Fats convinces Corky to kill his agent. Corky chases after Greene in the woods and bludgeons him with Fats' hard, wooden head and then attempts to drag the body into a lake. However, a still-living Greene suddenly lunges at him, causing Corky to drown him.

The next morning, Fats becomes even more possessive and jealous when Corky says that he plans to elope with Peggy and leave the dummy behind. Duke returns from his trip earlier than expected. Suspecting his wife has cheated on him, he wants to have a talk with Corky by the lake. Rather than confront him, Duke awkwardly confides to Corky that he loves Peggy and is worried about losing her. Duke suddenly spots Greene's body on the edge of the lake. Duke, believing Greene could still be alive, sends Corky to get help. Curious, he decides to search Corky's cabin, where Fats stabs him with a knife with "help" from Corky.

An increasingly deranged Corky manages to pull himself together and persuade Peggy to run away with him, but she insists on waiting to tell Duke face to face. She thinks everything is fine until Fats "comes alive" and reveals that Corky's card trick is only a ruse he uses to seduce women and that Peggy is only the latest of his conquests. Repulsed, she rejects Corky and locks herself in her bedroom. Fats says that, from this point on, he will make the decisions in Corky's life, immediately asserting this new authority by ordering Corky to kill Peggy.

Corky, turning on the charm and using Fats' voice, apologizes to Peggy through her locked door and leaves her a wooden heart that he carved. A short while later, Corky returns with a bloodstained knife. Fats seems pleased — until it is revealed that the blood on the knife is Corky's, who has fatally stabbed himself so that he will not kill anyone else. As a result, Fats also feels faint. They wonder which one of them will die first. Moments later, Peggy returns to the cabin, happily calling out that she has changed her mind and has decided to run away with Corky after all. As she speaks, she playfully changes her voice to impersonate Fats.