Davey Perkins, Kevin Brodie, a reporter, heads to the local precinct to chat with Sheriff Jones about a story, but the lawman insists that nothing newsworthy is happening tonight. At the same time, Dan Kester, Robert Easton, instead of keeping a revival appointment his wife Ev Leslie Parrish was expecting him to attend, spends the evening with Helga Christiane Schmidtmer, a waitress with a wary, knowing air. The night takes a sharper turn when Davey picks up his girlfriend Terry Diane Lee Hart, Ev’s sister, from the Kester farm, where Ev is unwisely drowning sorrows in drink. As they drive away, Ev’s inebriation worsens, and she ultimately orders a delivery from Dutch Bill Williams, the café owner, adding another layer to a night already thick with tension.
In a nearby junkyard, Davey and Terry share a private, intimate moment, while Dan, after his time with Helga, tunes into a revival broadcast on the radio and makes his way back home. A meteor crashes somewhere on the Kester property, sending out gusts of wind that crackle with electricity and trigger odd malfunctions. A B-52 bomber, on patrol, reports a magnetic anomaly just before it careens and crashes, its wreckage adding to the sense that something extraordinary is unfolding. Dr. Jenny Langer, an astronomer stationed at Montclair Observatory, alerts NASA about gamma-ray activity that seems tied to the meteor event, hinting at a cosmic disturbance just beyond ordinary explanation. At NASA, Dr. Vance, Steve Brodie, catches wind of the unusual signals and heads to Wisconsin to investigate the connection between the downed bomber and the gamma-ray phenomena. He teams up with Dr. Langer, and the two begin piecing together what is happening.
Meanwhile, the Kesters discover dead cattle on their land and come upon strange rocks near the meteor’s impact site. At the Kester house, Dan cracks open one of the rocks and unknowingly releases a spider from within, mistaking the crystal inside for a valuable diamond. Ev, heavily intoxicated, swats at spiders about the house, while Dan dismisses the insects as mere hallucinations. The drama takes a deadly turn when Dan stumbles upon a dead motorcyclist on the property, burying the body and hiding the bike to avoid drawing police attention. That night, Ev is attacked and killed by a giant spider, an early sign that the meteor’s gifts are far more dangerous than anyone anticipated.
The following morning, Davey carries the crystal to his cousin Billy, Paul Bentzen, who confirms that it is an industrial-grade diamond. With the missing motorcyclist now a mystery in town, the Sheriff intensifies his search near the Kester property. Dan returns to the meteor site and is killed by a giant spider, a savage turn of fate that amplifies the fear gripping the community. Billy, investigating further, meets a similar brutal end when a spider attack sends his car crashing into a gas station, culminating in a fatal explosion. Dr. Langer and Dr. Vance press on with their investigation, convinced that the mysterious rocks and the meteor hold the key to the carnage, and they believe the impact site is on the Kester property.
The Kester home is destroyed by the giant spider, though Terry survives the assault. Davey, unable to stop the creature with gunfire, manages to rescue Terry and rush her to the hospital. Langer and Vance, having barely escaped another encounter with the spider, inform Sheriff Jones of their findings, and Dutch immediately mobilizes a posse to chase down the threat. But the spider shifts its sights toward the town’s carnival, forcing the Sheriff to request National Guard support. As the danger escalates, Langer and Vance propose a radical plan: they deduce that the spiders likely entered Earth through a mini-black hole created by the meteor and arrange for a neutron device to be dropped at the meteor’s impact site. The plan succeeds, and the enormous spider is obliterated, dissolving into a puddle of ooze that marks the end of the immediate terror.
