Dr. Robert "Rack" Hansen, William Shatner, a veterinarian in rural Verde Valley, Arizona, is jolted by an urgent call when Walter Colby’s prize calf falls ill and dies soon after. He sends samples of the calf’s blood to a university lab in Flagstaff, hoping for answers, while the night sounds of the valley carry a growing sense of unease.
Diane Ashley, Natasha Ryan, an arachnologist, arrives with unsettling news: the calf didn’t die from a disease but from spider venom. Hansen meets the claim with skepticism, yet Ashley remains determined, insisting she wants to examine the carcass and the area where the animal sickened. The pair heads to Colby’s farm, where Birch Colby reveals their dog has also died from a massive spider venom injection. A chilling discovery awaits them—a sprawling tarantula hill on a back section of the land, a scene of countless arachnids clustered together in a disturbing display of collective survival.
Ashley theorizes that the tarantulas are converging in numbers because pesticides are wiping out their natural food supply, forcing cannibalistic spiders to band together to attack larger creatures. Hansen and Ashley return to Colby’s property with a plan to burn the spider hill, hoping to break the predatory migration. As they prepare, a bull on the Colby ranch is suddenly dragged into the chaos by a swarm of tarantulas, and Colby’s attempt to douse the hill with gasoline and light it ignites a dangerous escape route—many spiders slip away through a hidden tunnel. The next day, Colby is found dead, his truck overturned, his body trapped in spider silk. Hansen and Sheriff Gene Smith, David McLean, uncover the gruesome scene and realize the threat is rapidly spreading.
Venom samples test results come back, shocking in their severity: one tarantula venom is five times more toxic than usual. The town reacts with fear as the spider threat expands beyond the Colby farm. In response, the mayor Connors, Roy Engel, orders a sweeping pesticide spray across the hills and surrounding countryside. Ashley argues that a chemical fix would be only temporary, since the spiders would simply relocate along the same migration path to find new prey. She proposes a more balanced ecological approach—introducing birds and rats to restore the natural checks on the arachnid population—but the mayor dismisses the idea, worried that a flood of rats and the sight of many spiders could ruin the county fair.
A crop-duster is enlisted to spray the affected areas, but the airborne assault backfires in spectacular fashion when the pilot is attacked by tarantulas, sending the aircraft into a wild, uncontrollable flight that sprays residential areas with toxic chemicals before crashing. The consequences grow grimmer as the spiders begin attacking townsfolk, claiming Birch in a heartbreaking moment and taking Terri, Hansen’s sister-in-law, as another fatal casualty. Hansen rushes to the scene and rescues Terri’s daughter, Linda, who is left to cling to hope amid the danger. The survivors retreat to the Washburn Lodge, where the sheriff confirms that the arachnid strike has left Camp Verde isolated from the outside world. The plan crystallizes: load the last of the group into an RV and flee, but the spiders close in, trapping the lodge in their web of encroaching silk.
Smith drives into a town already under siege, only to be killed when another car slams into a support post beneath the water tower, causing it to topple onto his vehicle. Inside the lodge, a fuse is blown, plunging the building into darkness. Hansen climbs into the basement to replace the fuse, but the basement windows become a gateway for the spiders, and the ensuing venom sends him reeling upstairs where he faints, overwhelmed by the threat. As the survivors gather around a radio to catch any sign of help, the outside world remains oblivious—a cold, unsettling silence that underscores their isolation. When a battered Hansen finally pries boards away from a lodge window, he stares out at a nightmarish sight: the entire town of Camp Verde, and everything in it, is encased in shimmering spider silk cocoons, a quiet, suffocating end to the community they once knew. The scene lingers with a chilling sense that nature has claimed the valley, leaving only the silent, glistening aftermath behind.
