The film is about the residents of a small rural town whose inhabitants start to exhibit strange and violent behavior after a small earthquake ruptures the seal on a toxic waste burial site. The toxic material has migrated into the town's local dairy milk supply. Stuart, played by Tim Matheson, and his girlfriend Jennifer, played by Meg Tilly, come to the town to visit her hospitalized mother. The couple begin to notice increasingly odd behavior by several of the townspeople. Although Stuart drinks the local milk, Jennifer does not. As the day progresses, the townspeople and Stuart begin to exhibit signs of violent and extreme sexual behavior. Jennifer visits her friend Margo (Amy Stryker) where she observes evidence that she broke her son's arm. When Jennifer tries to leave in her car, she can't because the kids have slashed her ties. When she tries to leave in Margo's car, the kids trap her in the garage and set it on fire. Jennifer barely escapes with her life. The local doctor (Hume Cronyn) euthanizes Jennifer's mother then takes his own life. Stuart discovers that Jennifer's brother Eddie (Bill Paxton) harbors incestuous feelings for her and kills him. As the town descends into chaos and Stuart becomes violent, Jennifer flees in a pickup truck but gets stuck outside of town.
At the same time, Stuart escapes to the woods where he discovers the recently repaired toxic waste vault which he follows to the milk facility. He then begins to walk back to town, but comes across Jennifer in the stuck pickup truck. He helps free the truck, then warns her that as the only uninfected person she needs to leave. However, he intends to return to town to help as best he can. At the same time, the film shows two men loading a biplane with barrels of liquid. After the plane takes off, Stuart walks up to the other man whose government vehicle is filled with radios which talk about spraying the town. Stuart deduces this man has some connection to the events in the town, but when he confronts the man, the man shoots Stuart down with a shotgun. Jennifer, who had turned around to return to town, witnesses the man murder her boyfriend. She then runs down the mysterious man with her pickup truck and kills him. The movie ends with views of the town littered with corpses and a news item that government agencies have no explanation for the mass death of the entire town. The last shot shows Jennifer walking as the sun sets.
The film was directed by Graham Baker, and stars Tim Matheson, Meg Tilly, Bill Paxton and Hume Cronyn.