Following an atomic devastation in 1992, a man in a suit spills a parasitic specimen on Dr. Paul Dean. As the scientist is strapped to a gurney, an organism grows inside him and rips his body apart. Realizing the vision is a nightmare, Paul awakens in the front seat of his van and drives to a desolate, mountain-top village. When he encounters two men raping a woman, he shoots at the rapists with a laser gun and sets the woman free. She yells unintelligibly and escapes with one of her attackers. An old man thanks Paul for chasing the rapists away and introduces himself as Buddy. As Buddy prepares coffee, Paul develops a fever and excuses himself from the premises. Outside, he fights with the captive girl’s attacker, piercing his stomach with a pipe. Paul drives to the small town of Joshua and stops at a gas station marked with an “X” logo that matches the one on his van. He gives the station attendant a handful of silver in exchange for directions to a decrepit boarding house owned by Miss Elizabeth Daley. Paul attempts to give her cash for a room, but she refuses, asking instead for his gold ring. Upstairs, he sets up his scientific equipment and falls asleep until Miss Daley knocks on his door. Once awake, Paul opens his shirt to inspect a wound festering above his navel. Meanwhile, Wolf, a clean-cut member of the “Merchant” organization, arrives at the Joshua gas station to fill the tank of his sports car. When the attendant questions his method of payment, the man presents a silver card bearing the X logo. Paul visits the bar next door to the boarding house and exchanges his digital watch for a cup of canned soup. A gang of young rebellious outcasts and their leader, Ricus, enter and bully Paul until a young woman named Patricia “Pat” Welles delivers a bag of lemons for the bar owner, Collins. Ricus tells Collins about the “X” tattoo on his arm which he obtained while working for a corporation in the suburbs. In the boarding house, Miss Daley inspects Paul’s equipment and scientific books about parasites. Feeling sickly, Paul returns to his room and injects a fluid into his throbbing wound. Back at the bar, Ricus advances on Pat, but Collins comes to her defense wielding a gun. The gang discovers supplies in Paul’s van, raid his room, and take him captive to a warehouse. One of the gang, Zeke, opens a canister and unknowingly releases the parasite that has been ailing Paul. The scientist awakens hours later to find himself in Pat’s care. Meanwhile, Wolf questions Buddy and severs his hand with a laser beam for lying about Paul’s whereabouts. He then travels to Collins’ bar and drinks a glass of lemonade made from Pat’s lemons. Paul awakens again and insists on returning to town for his equipment. Pat tells Paul that she could have moved to the city following her father’s death, but she was afraid of being enslaved in a Merchant work camp. Wolf returns to the gas station to ask about Paul before barging into Miss Daley’s boarding house and demanding a room for the night. In the warehouse, the gang members surround Zeke, who lies with a large, leech-like creature attached to his chest. The parasite gnaws on Zeke’s collarbone, but Ricus is unable to cut it loose. Outside, Wolf watches as Paul picks up his supplies and drives away with Pat. As he follows them into the desert, the gang stops him and attempts a robbery. Wolf uses his laser to intimidate them, and escapes. As Paul and Pat carry his equipment to her house, he explains that he sustained his infection after creating a new strain of parasite for the government, which was working with the Merchants. He expects the dormant parasite to grow, and needs the specimen from Zeke’s body for research. If the organism reproduces, the specimen will release thousands of parasitic spores into the air. The next morning, Ricus finds that the parasite has disappeared after killing Zeke. When Dana awakens to find the wormy creature in her sleeping bag, she attempts to sneak away, but it latches onto her leg with its teeth. The gang bring her to Miss Daley’s boarding house, where she and Collins suggest finding Paul. As Paul leaves Pat’s house to look for the mutating parasite, Wolf attacks Pat in her garden for refusing to reveal Paul’s location. Just then, Ricus arrives and knocks Wolf unconscious, but discovers the house is empty and leaves. When Paul returns, Pat describes her attacker, and Paul identifies him as Wolf, a government liaison. Paul now realizes that he can kill the parasite with high-frequency sound waves, but he must first extract a sample from the growing specimen now attached to Dana. In the boarding house, Dana dies, and the creature attacks Miss Daley. She convulses until her body decomposes and the parasite bursts through her skull. Pat and Paul enter the room and wrangle the parasite to inject it with a fluid. Collins descends to the basement, where he is attacked by Wolf. Although Ricus attempts to stop Wolf, the Merchant kills him. As a radio transmitter produces high-pitched sonic waves, the parasite in Paul’s abdomen breaks free from his flesh. It jumps on Pat’s arm, but dies before it can puncture her skin. Wolf tackles Paul as he runs upstairs to kill the larger parasite; the creature sinks its teeth into Wolf’s face, and he tumbles over the balcony onto a gasoline tank outside. Pat shoots at the tank, causing it to explode. Pat, Collins, and Paul watch as the flames consume Wolf’s corpse and destroy the parasite.