As the chilling events of this horror saga unfold, a United States military convoy is tasked with transporting a hazardous load of Trioxin barrels. However, one miscalculated move sends a barrel tumbling into a river, unnoticed, leading to catastrophic consequences. The next day, a trio of mischievous pre-teens—Johnny, Billy, and Jesse Wilson—embark on an ill-fated adventure to an abandoned cemetery mausoleum. Here, they stumble upon a long-forgotten barrel hidden beneath the storm drains and, upon prying it open, they uncover a horrifying sight: a dead body, a clear signal of doom on the horizon. As the toxic gas begins to escape from the container and infiltrate the air, Jesse suggests reaching out to the military for assistance, but his friends abandon him, leaving him isolated in the mausoleum.
Meanwhile, the nefarious Trioxin continues to seep into the cemetery, as both Billy and Johnny return to the ominous barrel, unknowingly worsening the already dire circumstances. Soon, grave robbers Ed and Joey, alongside Joey's girlfriend Brenda, arrive in their van, unwittingly kicking off a chain of disastrous events. While Jesse makes his desperate escape, he leaves his friends to face the vile effects of Trioxin alone.
With each passing moment, the situation escalates. As acid rain begins to saturate the ground, the world around them buckles as corpses reanimate with alarming speed. Back home, Jesse is assigned homework by his sister Lucy (character not specified), but seizing a chance during a cable repairman’s visit, he stealthily makes his way to Billy's house. Upon arrival, he finds Billy suffering the tormenting effects of Trioxin, and in a chilling moment, Billy warns Jesse to keep their grim discovery a secret from others.
Determined, Jesse heads back to the sewer to investigate the barrel, confronting a grotesque tar-covered zombie that epitomizes the nightmares lying in wait. He races back to the cemetery where the recently resurrected dead are clawing their way from their graves. Inside the mausoleum, Ed and Joey are captivated by the unsettling sight of a reanimated corpse, their fascination quickly morphing into sheer terror as they bolt for safety, colliding with Brenda, who is desperately trying to evade the growing horde. It's clear that their hopes of escaping unscathed are dwindling into a frantic fight for survival against the rising tide of undead.
Once back home, Jesse frantically relays his grave concerns to Lucy, but he is met with disbelief. Eager to escape, he concocts a clever plan to set off the smoke alarm, which provides him the diversion he needs. His next objective is to get in touch with Colonel Glover from the military; unfortunately, their dialogue is abruptly interrupted due to unfortunate technical issues.
Meanwhile, the trio of Ed, Joey, and Brenda embarks on a perilous mission by stealing Tom's van in a desperate attempt to outrun the relentless zombies. Yet, their fortune turns when they find themselves trapped among the undead, forcing them to seek a new refuge. Back at Jesse's home, matters worsen as Ed starts to show disturbing signs of Trioxin affliction, while the relentless zombies close in on their location, driving the survivors into a panic as they scramble for escape.
In another corner of town, Billy's life spirals out of control when his father becomes another victim of the living dead. Tragically, his mother encounters her resurrected husband, resulting in a harrowing confrontation with her very own son who has transformed into a mindless creature. Meanwhile, Jesse, Tom, and Lucy head towards Lucy's grandfather's house, where they amass weaponry for the upcoming confrontation with the zombies.
Their journey leads them to an empty hospital emergency room, providing a fleeting moment of peace before the peace shatters as Ed and Joey begin exhibiting signs of rigor mortis—a harbinger of their doom. Jesse grapples with his deepest fears when he finds himself under attack by a zombie that has inexplicably survived prior gunfire.
As Jesse, now joined by Joey and Ed, escapes in a doctor’s car, their path crosses with National Guardsmen, who mistake them for the undead, triggering mass panic as the soldiers open fire. In the chaos, Brenda tragically abandons her friends and flees with Joey in a stolen ambulance, only to find herself ensnared as Ed becomes the next victim of his friend's monstrous transformation.
With every avenue of escape growing narrower, Tom maneuvers the group to a nearby meatpacking plant, where they commandeer a truck filled with brains—an audacious strategy aimed at trapping the ravenous zombies. In a desperate twist, Billy, still reeling from his own transformation, unwittingly creates the opportunity for their risky ploy. Jesse empowers the power plant’s generators, brilliantly electrocuting the ravenous undead, but in the aftermath of this macabre victory, Billy makes a futile lunge towards Jesse only to be fatally struck by a transformer that seals his fate. Ultimately, Colonel Glover and his men arrive, tasked with containing the chaos and escorting the living away from this grim battlefield.
