In October 1962, teenager Gene Loomis (Simon Fenton) and his younger brother, Dennis (Jesse Lee), move to Key West, Florida, when their father is deployed to work on a submarine just off the naval base. Shortly after their arrival, a televised speech by U.S. President John F. Kennedy announces the threat of an impending nuclear attack from Cuba, and panic strikes the nation.At school, Gene and his classmates perform an air raid drill by crouching in the hallways, but an outspoken liberal student named Sandra (Lisa Jakub) refuses to participate and warns her peers about the real dangers of radiation.Gene bonds with a boy named Stan (Omri Katz) over his love of horror films, and the two make plans to see B-movie producer Lawrence Woolsey's latest feature, Mant, about a man who has been transformed into an ant as a result of an atomic mutation. Stan introduces Gene to his crush, Sherry (Kellie Martin), and encourages his new friend to invite a girl to the screening.Later, Gene and Stan watch as frightened townspeople swarm the grocery store frantically purchasing food to prepare for imminent nuclear destruction. Gene's mother (Lucinda Jenney) suggests he distract Dennis by taking him to see a light-hearted comedy film at the local movie theater. Bored, the boys walk out of the screening and encounter two men named Herb (Dick Miller) and Bob (John Sayles) protesting Mant's tactless subject matter. Lawrence Woolsey (John Goodman) appears among the crowd of onlookers, having recently arrived in town to promote the picture. He hands out a stack of free passes so the citizens can decide for themselves whether or not his films should be considered objectionable. At home, Gene looks through his horror movie magazines and recognizes one of the protesters as Herb Denning, a minor player in Woolsey's pictures.The next morning, the seemingly wholesome Sherry tells Stan about her former relationship with an older guy, a juvenile delinquent named Harvey Starkweather (James Villemaire). Seeing Sherry with Stan, the angry and jealous Harvey corners the boy and threatens him if he pursues the relationship. Meanwhile, Gene strikes up an awkward conversation with Sandra, who received a week of detention for acting out during the air raid drill.After school, Gene asks Woolsey about Herb Denning, and the filmmaker explains he hired him to stir up interest in the movie, never expecting he would be recognized. In preparation for the screening, Woolsey outfits the theater with electric buzzers, smoke machines, and earthquake simulators, hoping his "AtomoVision" and "RumbleRama" experience will exploit the heightened sense of fear gripping the audience.Meanwhile, Harvey has a run-in with Herb and Bob and attempts to steal money from them, only for the two men to rough up Harvey to get their money back. Harvey decides to look for a real job to earn money to win Sherry back.That night, Stan makes up an excuse to cancel his date with Sherry, but Sherry's younger brother blackmails her into seeing Mant with him instead. On Saturday afternoon, Gene, Dennis, and Stan join the long line outside the theater. When Sherry arrives with her brother and sees Stan with his friends, she reprimands him for lying to her. Inside, Woolsey's muse, Ruth Corday (Cathy Moriarty), poses as a nurse and forces the attendees to sign liability agreements, warning that the film may "scare them to death."Gene sees Sandra across the lobby and offers to sit with her, while Harvey Starkweather is recruited to control the special effects switchboard during the screening. Once the film starts, theater chain owner Mr. Spector (Jesse White) watches in delight as the gimmicky effects cause the audience to scream. Gene runs into Sherry in the lobby and explains Stan's evasiveness, which prompts Sherry to apologize.During a particularly scary scene, Harvey sneaks into the theater wearing a "Mant" suit and terrorizes the audience, but becomes enraged when he sees Stan and Sherry kissing. Harvey attacks Stan and flees, but the children chase him downstairs to the basement and find the paranoid theater manager's fully equipped fallout shelter. Gene unknowingly activates the door, which locks before he and Sandra can escape. Hearing the thundering effects of the film upstairs, the two mistakenly believe an atomic bomb has already been dropped and fear they are the only survivors responsible for carrying on the human race. They kiss, but are interrupted when Woolsey, Gene's mother, and Sandra's parents break down the door and see the two teens in a romantic embrace.As part of his costumed performance as "Mant," Harvey grabs Ruth Corday and drags her out of the theater holding a knife at her throat. Backstage, he demands compensation for the job and kidnaps Sherry. During the climactic scene of Mant, Woolsey and Gene notice the upper balcony is about to collapse due to the excess weight of too many people on the balcony, but the audience is convinced the world is ending and quickly scrambles to get out of the theater before disaster strikes. Dennis, however, remains trapped upstairs as the balcony detaches from the wall. Gene runs to help, and slowly coaxes his brother to safety. Outside, police arrest Harvey, and Sherry kisses Stan. When the audience realizes they have not been bombed, they delight in the experience and demand to see the film again, unaware the venue has been destroyed. Mr. Spector congratulates Woolsey on his success and eagerly begins brainstorming ideas for their next sensationalist picture.Sometime later, the Loomis family is relieved to learn that the Cuban Missile Crisis has ended and their father will soon return. Gene and Sandra say goodbye to Woolsey and Ruth, who drive to their next opening in Cleveland, Ohio.