After a university lecture on unknown humanoid creatures such as Bigfoot and the Fouke Monster, two University of Chicago students, Pahoo Dennis Fimple and Rives John David Carson, decide to spend their spring break chasing the legend, driving from Chicago toward the Louisiana–Arkansas border. There they begin interviewing witnesses, starting with a family whose car crash was spurred by the creature, killing the parents of a young child named Orville Bridges Jim McCullough Jr..
Pahoo and Rives stay with Orville and his grandparents, who are wary of being painted as superstitious rednecks but soon warm to the students. Grandpaw Bridges Dub Taylor regales them with stories of encounters with the creature, including a nightmarish memory of it viciously murdering his pet dog. Late in the night at the family's rural farm, the house is awakened by sinister, guttural screams from the woods, and Pahoo and Rives hurry to document the sounds with a tape recorder in hopes of proving something real.
At a local diner, the two men meet two local women, Becky Carter Becky Smiser and Michelle Michelle Willingham, who take a clear interest in the visitors. The women invite them to come to their campsite that evening in the nearby state park. Not long after Becky and Michelle arrive, the group is hunted by the creature, which stalks them outside the tent during a heavy rainstorm. Moments later, Sheriff Billy Carter Bill Thurman bursts into the tent, orders the girls to leave, and instead arrests Pahoo and Rives, locking them up in the county jail.
Nearby, Joe Canton Jack Elam is confronted by the creature in his backwoods shack. He defends himself with a rifle, and when he staggers into the police station raving about the monster, Sheriff Carter dismisses him and holds him overnight in the same cell as the two students. Canton recounts his first encounter with the creature years earlier, when it dragged his friend Willy into the lake and killed him.
Dawn brings a release on the condition that Pahoo and Rives leave town. They refuse to bow to the orders and instead accompany Canton back to his home to learn more about his encounters with the creature. Canton guides them to a remote area deep in the swamp where he found the creature’s tracks. That night, they explore the swamp, and Pahoo is viciously attacked by the creature while Rives waits in their van. The creature raids their campsite again before Rives radios the local police. Moments later, the creature attacks the van, sending it tumbling down a slope with Rives inside. Rives fires at the creature as the van explodes, and he escapes into the swamp, where he locates the injured Pahoo, who falls into a coma.
Carter arrives at the scene with Canton, who agrees to help. At dawn, they locate Rives and Pahoo, who is on the verge of death, and rush them to the hospital. Pahoo receives treatment for critical injuries, and when Rives pleads at his bedside for his survival, Pahoo regains consciousness. He jokes with Rives that, even in pain, he is only regretful that the men will have to restart their project.
