Teenage Amy Harper dates Buzz Dawson for the first time and they go to the carnival with their friends Richie and Liz. They smoke grass and have a good time visiting the attractions including a sideshow with freak animals. The silly Richie suggests the group to spend the night in the Funhouse for fun. During the night, they witness the murder of fortuneteller Madame Zena by a man wearing a Frankenstein mask from an opening in the ceiling of a room. They decide to leave the funhouse but all the exits are locked. Meanwhile, Richie sneaks into the room and steals the funhouse manager's money. The masked man returns with his father and owner of the funhouse to show the corpse of Madame Zena; when the man realizes that he had been robbed, he presses his son, who removes the mask and shows his horrible face. Richie starts and drops his lighter in the room. The owner asks his freak son to chase the thieves and eyewitnesses in a night of terror for the teenagers.