As teenager Amy Harper prepares for her first date with Buzz, her younger brother, Joey, a horror aficionado, scares her by reenacting the shower scene from the film Psycho. Furious, Amy vows to get even. Although Amy’s parents warn her to stay away from the traveling carnival because two children died near the carnival grounds in another town, Buzz convinces her that it will be fun. They double date with Richie and Liz, who are equally excited to see the carnival. Joey sneaks out of the house and also heads for the fairgrounds. There, the four teenagers smoke marijuana cigarettes, enjoy several rides, see a magic act, peep into the strip show, check out the side show freaks, and tease Madame Zena, a fortune teller. When Richie convinces them to spend the night in the funhouse, Amy calls her parents to say she is sleeping over at Liz’s house, and the four climb into the funhouse cars. Joey sees them go into the funhouse, but the cars come out empty. Seeing Buzz’s car in the parking lot, Joey decides to stay. Meanwhile, inside the funhouse, the four teenagers walk amongst the spooky mechanical characters before settling down for romance. They are disturbed by a sound, and see lights go on in a room beneath the funhouse. The teenagers watch through the floorboards as a carnival worker wearing a “Frankenstein” mask takes $100 from a cashbox and pays Madame Zena for sex. The “monster,” however, is prematurely excited and Madame Zena laughs. He wants his money back and, when she refuses, he slams her into an electrical panel and the lights go out. The masked “monster” murders Madame Zena and leaves as the teens panic and look for a way out. When they reach the room below, Richie insists on going inside alone to verify that Madame Zena is dead. The teens reach the outer door, but it is locked and cannot be opened. They find the front door is also locked, and search for another escape. Meanwhile, the “monster” returns to his room with his father, the freak show announcer, or “barker,” who says he had no problem covering up his son’s previous murders, but is furious that his son killed a member of the carnival. The teens watch from above as the barker decides to bury Madame Zena and blame the death on the locals. As the barker yells at his son for paying so much money to Madame Zena, he opens the cashbox to return the cash, but finds it is empty. The barker screams at his son for stealing the money and yanks off the Frankenstein mask, revealing a hideously deformed face beneath. The “monster” can barely speak, but he manages to communicate that he did not steal the money. Buzz realizes that Richie stole the money when he was supposedly checking on Madame Zena. As Richie admits the theft and offers to share the money, he accidentally drops his lighter through the floorboards and the barker realizes others are in the funhouse. The barker tries to cajole them into revealing themselves, but the teens remain mum, knowing they are in danger. Meanwhile, Joey approaches the funhouse and looks beneath the front entryway for a way in. At that moment, the “monster” reaches out to grab him, but Joey barely manages to get away and collapses into the arms of a friendly carnival worker. Inside the funhouse, the power comes back on. It is still dark, but lightning flashes and the mechanical creatures move. Realizing the barker and the “monster” plan to kill them, the teens pull axes and knives from wall displays. Suddenly, a noose slips around Richie’s neck and pulls him up and out of sight. A short time later, Joey is asleep in the carnival worker’s trailer when Mr. and Mrs. Harper arrive to pick up their son. Back in the funhouse, Amy, Buzz and Liz are frightened as someone rides through the shadows toward them. As the car nears, Buzz assumes it is the “monster” and buries his axe in the person’s head, only to discover it is Richie. When Liz falls through a trap door that slams shut behind her, Buzz and Amy unsuccessfully try to open the hatch. As Amy looks outside through a fan vent and sees her parents carrying Joey to their car, she screams for help, but her parents cannot hear her over the fan’s motor. Joey, still in shock, stares at the funhouse and remembers his sister’s threat to get even with him. Amy keeps screaming, but her parents drive away. On the floor below, the “monster” approaches Liz as she reaches for her knife. She offers to have sex with the “monster” and when he grabs her, she stabs him in the back. However, the “monster” kills Liz as he struggles to yank the knife out. Meanwhile, on the funhouse floor, the barker holds Amy and Buzz at gunpoint, but Buzz attacks him. They fight until Buzz shoves the barker into a knight’s lance and shoots him with the gun. When the “monster” arrives and sees his father dead, Buzz yells for Amy to run, then turns to fight the monster alone. Amy races through the funhouse and, moments later, Buzz’s dead body moves through the ride toward her. She runs to the floor beneath the funhouse and hides among the machinery. The “monster” stalks Amy until she trips, grabs an iron pole and shoves him against an electrical panel. Although he is electrocuted, the “monster” does not die. As a hook latches into his clothing and pulls him toward two large gears, the “monster” grabs Amy, but she struggles to free herself as they are pulled into the machinery, breaking away just as the “monster” is killed between two grinding gears. Amy staggers out of the funhouse in the early morning light.