Set in an undeterminate year in the far future, a nuclear war in 1992 has reduced the world to poverty. Instead of a government, America is run by an organization called the Merchants, who exploit the degenerate remains of society. (Silver coins and bullion is used as currency, what food that is available is rationed, and gasoline costs an upwards of $40-per-gallon for super-unleaded). In order to keep control of the populace, the Merchants force Dr. Paul Dean (Robert Glaudini), a scientist living in the ruins of Los Angeles, to create a new life form, a parasite that feeds on its host. Realizing the deadly potential of such a being, Dean escapes from the Merchant-operated laboratory with the parasite, accidently infecting himself in the process.
Now on the run, Dean travels from town to town in a stolen ambulance, studying the parasite that he keeps in a large silver cannister so that he can find a way to destroy it, as well as the one of the parasite's spawn that is growing on the inside of his abdoman, all the while keeping one step ahead of a Merchant named Mr. Wolf (James Davidson) who is hunting for him.
While resting in a desert town, he is attacked by a gang of hooligans (Cherie Currie, Freddy Moore, Natalie May, Joanelle Romero, Tom Villard) led by Ricus (Luca Bercovici), a former slave of the Merchants. The gang steals the silver cannister containing parasite, not realizing what it is, and it breaks out and infects one of the members which the parasite slowly eats the thug from the inside out.
Meanwhile, Paul befriends a pretty young lemon grower named Patricia Wells (Demi Moore), who promises to help him destroy the escaped parasite. Ricus, trying to save the life of his friend, comes to Paul for help, only to be confronted by Wolf. Patricia, Paul, and Ricus manage to evade Wolf, but when they return, the parasite has spread to another member and grown into a fleshy worm with a mouthful of deadly teeth. After luring out and killing the parasite in Paul (which is brought out by a surge of an electrical current), the main parasite worm attacks Wolf, who is then blown up by Patricia, Paul, and Ricus at the local gas station, apparently killing it for good.