A man driving along a lonely back road at night is suddenly startled by what he sees and is promptly killed by something that crashes through his windshield. The next day, in the nearby town, teenagers Carol (June Kenney) and Mike (Gene… More A man driving along a lonely back road at night is suddenly startled by what he sees and is promptly killed by something that crashes through his windshield. The next day, in the nearby town, teenagers Carol (June Kenney) and Mike (Gene Persson) decide to go looking for her father, who didn't get home last night. They find his wrecked truck and enter a nearby cave to begin searching for him. They find his blood-covered hat and other signs of human remains. As they go deeper inside, they suddenly get trapped in a huge web, then they spot its maker -- a spider the size of a small house. They manage to escape and alert the county sheriff (Gene Roth), who doesn't take them seriously, but does heed the warning of Mr. Kingman (Ed Kemmer), the science teacher at the local high school, who brings along a pest-control crew along with his deputies and a tanker loaded with DDT. They encounter the creature, and, after losing one of their men, dispatch it with the insecticide. Kingman persuades the sheriff to bring the carcass into town so that he can arrange to have it studied, leaving it in storage at the high school recreation room for lack of anywhere bigger to keep it. As it turns out, the creature isn't dead, just stunned, and as the local rock & roll band rehearses, the giant spider comes to bloodthirsty consciousness, breaking out of the building and ravaging the town. Bullets won't hurt it -- as Kingman says, you could punch holes in it all day without hitting a vital spot -- and the town is soon cut off as the telephone lines are down. They get one break when the creature heads back to its cave. What the sheriff and Kingman don't know is that Carol and Mike are also out at the cave, searching for a memento from her father. The plan is to seal the cave up forever, or even bring the whole cavern down with TNT, but once they find out that the kids are in there, they know they've got to go in to find them, which means killing the spider outright. That's when Kingman devises a plan to electrocute the spider, if they can get to it before it disappears too deeply inside the caverns, and in time to save the two teenagers.