In a small American town, high school science teacher Mr. Kingman is approached by a pair of his students, Mike and Carol, who report an unusual discovery. During an afternoon outing, they stumbled upon what seems to be a giant spider lurking in a local cave. Initially hesitant, Kingman is intrigued enough to investigate further. The group expands to include a third student, Joe, and the small party makes their way to the cave to gather evidence of the unimaginable creature they claim to have encountered.

Upon arriving at the cavern, their skepticism is shattered when confronted with the monstrous arachnid in the flesh. After a harrowing escape, the quartet convinces the town's authorities to take action. The townspeople, though incredulous, set out to deal with the gigantic spider, resolving on a plan that they believe will ensure their safety. However, a series of unforeseen circumstances results in the spider being inadvertently forced into a different environment, where it becomes an even greater threat to the unsuspecting community.