In a small, swampy Florida town, unsettling events begin to unfold when locals start mysteriously disappearing. Steve Benton, a game warden, teams up with his girlfriend Nan Grayson to investigate these strange occurrences. The sleepy town is thrown into turmoil when Dave Walker, a local shopkeeper, discovers his wife Liz is having an affair with Cal Moulton, a trapper. His discovery drives him to desperate actions, leading them to a confrontation by the swamp. Soon after, residents go missing, prompting Steve and the local authorities to intensify their search efforts.

As they delve deeper into the murky waters of the swamp, they become aware of reports of gigantic leeches lurking in the depths. Suspicion grows as the town's fear heightens, drawing them to question the safety of their once quiet home. Despite skepticism from local officials, Steve is convinced that the mysterious creatures are responsible for the disappearances. Meanwhile, tensions in the community rise as more people go missing, prompting a sense of urgency. With the stakes higher than ever and mounting pressure from worried townsfolk, Steve plans a daring effort to confront the source of the menace.