On July 3, 1984, at the Uneeda Medical Supply Warehouse in Louisville, Kentucky, foreman Frank tries to impress new employee Freddy by showing him military drums of a toxic gas called Trioxin. The drums, long stored in the basement after a delivery error years earlier, become the focus of a dangerous accident when Frank strikes one to prove its seal. The gas spills out, seemingly melting the cadaver inside and reanimating another body kept in a meat locker. What follows is a troubling demonstration: the reanimated cadaver is just the beginning, because every fragment of the zombie’s body can survive on its own. In a desperate attempt to end the threat, Burt, their boss, arranges for the zombie to be incinerated at a nearby mortuary crematorium with the help of his friend Ernie. The plan backfires in a shocking way—cooking the creature unleashes the same toxin into the air, and a toxic rain begins to fall, capable of reanimating corpses in nearby cemeteries.
While this nightmare unfolds, Freddy’s girlfriend Tina and his friends Spider, Trash, Chuck, Casey, Scuz, and Suicide head to the cemetery to check on Freddy. Trash begins a reckless display on a gravestone, while Tina accidentally wanders into the warehouse basement and runs into the disfigured reanimated cadaver from the barrel. The rest of the group arrives soon after and manages to rescue her, but Suicide loses his life in the struggle. Casey realizes she saw Freddy entering the mortuary, and the group makes its way toward him through the cemetery, only to be met by a growing wave of zombies. Trash is killed in the chaos, and Chuck and Casey flee back to the warehouse, leaving Spider, Tina, and Scuz to push onward to the mortuary. There, they discover Frank and Freddy growing increasingly ill from exposure to the gas, and the paramedics’ tests reveal a chilling paradox: they appear conscious, yet are clinically dead. The dead begin to rise from the mud—Trash, submerged in chemical-laden sludge, comes back as a zombie and begins to hunt and feed. News of the dead rising spreads quickly when Burt and Ernie learn of the situation at the cemetery and barricade the mortuary.
The siege intensifies: Scuz is killed while protecting the barricade, and the zombies overwhelm the evacuation routes, devouring paramedics and police who arrive on the scene. The survivors manage to restrain one particularly menacing zombie on the mortuary table, and she explains that the reanimated can feel themselves decaying. She also reveals a startling survival mechanism: feeding on the brains of the living temporarily eases the pain of being dead. With Frank and Freddy showing more and more signs of becoming undead, Burt confines them in the chapel, keeping Tina with them because she refuses to abandon Freddy. A horrifying moment follows when Freddy, driven by hunger, tries to attack Tina, and the trio—Burt, Ernie, and Spider—rescue her by reopening the chapel and blinding Freddy with a strong acid. In the ensuing chaos, Frank escapes and, still able to control his mind, commits suicide by stepping into the cremator. Burt and Spider race back to the mortuary in a police car, but the onslaught of the zombie army—led by Trash—forces Burt to abandon Ernie and Tina. Ernie and Tina hide in the attic as Freddy, blinded but relentless, claws at the door.
Desperate for a solution, Burt and Spider return to the warehouse and reunite with Casey and Chuck. After immobilizing the basement zombie—whom Spider names “Tarman”—they attempt to contact the police, only to learn that the force has been overrun by the undead. With no immediate help available, Burt makes a critical call to the number on the drums, which connects him to a military officer, Colonel Glover. The Colonel informs him that the area has been deemed a target for destruction to halt the invasion, and Louisville is set to be wiped out with nuclear artillery on the morning of July 4. The survivors are caught in a frantic scramble as the town’s fate is sealed; Burt and the others are killed in the nuclear blast, ending the immediate threat to them but not the wider threat of Trioxin.
In the grave aftermath, Colonel Glover discusses the mission with his commanding officer and states that the result is as planned—only a small area is destroyed, and casualties are limited. Yet this restraint comes at a grim twist: fires from the nuclear blast release trioxin into the atmosphere in a broader arc than before. The film ends with the ominous sound of fires burning and the rain of toxic droplets beginning again, while zombies cry out from their graves. The implication is clear: the invasion is far from over, and the threat of reanimation will resume as the toxic rain begins anew.
