Following the title sequence, a comet or meteor is seen streaking across the night sky. Davey Perkins (Kevin Brodie) stops in to see Sheriff Jones (Alan Hale, Jr.). He works for his Dad's newspaper and is looking for a story. The Sheriff informs him that things are quiet.At a rundown farm outside of town, Dan Kester (Robert Easton) bids his wife Ev (Leslie Parrish) goodbye. He tells her he's going to a revival meeting. The preacher (Tain Bodkin) is giving a sermon to the faithful, but Dan isn't there. Davey stops by the Kester place to pick up his girlfriend, Terry (Diane Lee Hart) and greets Ev on the porch. She is drinking and offers Davey one. Ev and Terry are sisters. Terry and Davey depart, and Ev continues to drink alone. Ev runs out of alcohol and calls Dutch, the café/bar owner and asks him for a delivery. Davey and Terry drive over to a local junkyard and start necking. Dan finishes up with his prostitute/waitress, Helga (Christiana Schmidtmer) and leaves her place and drives home, listening to the revival on the radio. Just as Dan arrives home the meteor crashes somewhere on their property. In addition to a strong wind, electrical equipment starts to malfunction.A B-52 flying on patrol reports a magnetic anomaly and RADAR problems, then crashes. The Sheriff starts getting calls from citizens reporting electrical problems. Dr. Jenny Langer (Barbara Hale) at Montclair Observatory calls NASA again to report further information, now including gamma ray activity. At the Houston office of NASA, Dr. Vance (Steve Brodie) is feeding and talking to his plant. A co-worker, Paul, brings him some reports from Northern Wisconsin. Vance suspects the downed B-52 and the reports are related. Vance leaves for Wisconsin to investigate.Langer finishes a lecture on astronomy to her class when Dr. Vance arrives on campus to meet with her. They walk back to her office and she briefs him on her findings. The Kesters search their property and find a dead cow. In fact they find many dead cattle. Kester proposes to butcher the animals and sell the meat to the local café. As they continue to survey their property, Ev picks up a strange rock. They find more of the same kind and collect them. They finally arrive at the impact spot of the meteor.Sheriff Jones walks into the local café/bar and talks to the owner, Dutch (Bill Williams) and the waitress, Helga. Helga goes into the kitchen to get the Sheriff his breakfast. The Kesters return to the house. Dan tries to break open one of the rocks, but it falls off the table onto the floor, and the geode breaks open. Unobserved by the Kesters, a spider crawls out. Dan retrieves the rock and pulls a crystal out. They are convinced they are diamonds after Dan scrawls a dollar sign on the kitchen window. Back at the café, Langer and Vance stop by to see the Sheriff. Davey stops by and joins the three at the table. He's still looking for a story. Davey tells them about the electrical disturbance and wind the evening before.Ev is hitting the booze pretty heavily and swatting the spiders on the kitchen table with a flyswatter. Dan hasn't seen them yet and attributes Ev's spiders to the DT's. Dan heads back out to collect more rocks, but discovers the dead body of a motorcycle rider. Instead of reporting his find, he buries the body and hides the motorcycle. He doesn't want the Sheriff nosing around the property and finding either the diamonds or the pot they are growing. He returns to the house and tells his wife, Ev of his discovery. That evening, Ev, still drinking, goes to bed, but can't get to sleep. As she pulls open a dresser drawer to get something, a giant spider jumps out at her. She exits the bedroom and the house, screaming, and runs into an out building or barn. There she is attacked by a dog sized spider that kills her.Dan leaves Helga's house the next morning and drives into town to see his cousin, Billy (Paul Bentzen). Billy is a rock shop owner and examines one of Dan's crystals. Billy pronounces them inferior--industrial quality, but still a diamond. Dan drives back home. The Sheriff stops by the Kester farm to make inquiries about the missing motorcycle rider. Dan lies to the Sheriff and denies any knowledge. After the Sheriff leaves, Dan heads back to the impact zone to dig for more rocks. He is attacked and eaten by a gigantic spider, the size of a car. His curiosity whetted, Billy stops by the Kester place to talk to Dan a little more about the diamond, but Dan is missing. He leaves, but on his way home his car hits a huge web, and he is attacked by the gigantic spider. He manages to escape, but in his confusion runs his car into a gas station, and the explosion kills him.Langer and Vance drive around trying to locate the impact zone. They know its around the Kester property, but not an exact location. Meanwhile the Kester house is destroyed by the giant spider with Terry inside. Davey arrives at the house, only to find it demolished. He fires his rifle at the departing spider, then rushes to retrieve Terry who is barely alive. The bullets seemed to have no effect on the spider. Vance and Langer are attacked, but manage to escape the giant spider. Davey takes Terry to the hospital. Langer and Vance make it back to town and inform the Sheriff of the 50-foot spider. The Sheriff gives them a couple of rocks to examine. Davey calls the Sheriff to report the damage at the Kester place and Terry's condition. Dutch organizes a posse to go after the giant spider, but the Deputy orders them home. The mob ignores the order and heads for the Kester place.The giant spider attacks the Gleason Days carnival. The Sheriff is called by Gleason officials and told the spider is headed his way. He calls for the National Guard. Vance and Langer had discussed earlier the possibility of using a neutron device to destroy a mini-black hole that allowed the spiders to invade our planet. The neutron device is shipped to the local airport and loaded on a helicopter. The target is the impact site. Meanwhile, the mob gathers and Sheriff Jones tries to keep them off the Kester property. The spider attacks the mob while they are still in town. The giant spider returns to the impact site, where Langer and Vance direct the dropping of the neutron device. The spider attacks the deputy who is eaten alive. The neutron device is deployed and the giant spider melts into a pile of goo.
Storyline
A black hole hits North Wisconsin and opens a door to other dimensions. Giant 15 meter spiders emerge from it, who have an appetite for human flesh! Dr. Jenny Langer and Dr. Vance from the NASA try to save the world. — Tom Zoerner