The film opens in 1986 with a frightened Les Daniels forced into a snake-handling ceremony. When he’s asked to hand one of the snakes to his father, he hesitates, giving the creature just enough time to strike and sever his father’s artery. The father dies within minutes, leaving a young boy haunted by fear and a heavy sense of guilt that lingers into adulthood.
Twenty years pass, and the same phobia still grips Les, compounded by the memory of his role in his father’s death. His older brother, Duff Daniels, needles him about it, creating tension between them. In an effort to help him overcome the terror, Duff visits a Native American snake proprietor, Screaming Hawk. Hawk introduces them to a small snake kept in a jar on his desk: Unteka. The legend says Unteka is a relic of an ancient lineage, capable of rapid growth and responsible for violence against the tribe in the past. Hawk lays out three rules for Duff: don’t let it out of the jar, don’t let it eat anything living, and never fear the heart of the snake. Despite being told he cannot have Unteka, Duff steals it.
Back home, Duff accidentally breaks the jar. Les, who witnesses the creature’s rapid growth, is dismissed as his brother panics. Later that night, Unteka emerges from the confinement and consumes the family’s pet cat, then begins slaughtering livestock in the coop. When Duff’s mother investigates, she, too, becomes a casualty. Duff seeks help from local exterminators, who explain that if the snake isn’t yet fully grown, it can be killed by striking at its head. Duff makes the attempt, and it seems to work—until Unteka revives the next night and kills Duff and the family dog.
Les returns home after a rough night, finding the house ransacked. He phones his police officer girlfriend, Erin, and her ex, the chief, Bo. Les insists he suspects foul play and fears the family may be dead, which only deepens Bo’s suspicion that Les might be the killer. Unteka then attacks a vacationing family in the woods, killing the father and injuring others who take shelter in a van. Erin arrives, reviews the scene, and concludes the family may still be alive, prompting her to investigate further with Screaming Hawk to learn more about the monstrous snake.
Soon the police and searchers confirm that Unteka is real and in pursuit. Bo and his team move to stop it, but the creature proves formidable, knocking him down and turning the extermination effort against them. Meanwhile, Les, Erin, and Hawk intensify their search for Unteka’s current whereabouts. The snake has grown monstrous, reaching about 70 feet, and it heads for the county fair, where a guest appearance by the actor who brings the comic figure Feedback to life is about to thrill the crowd.
Unteka slaughters several attendees, including Fay, before forcing its way into the rides area. Feedback manages to fend it off long enough to guide frightened spectators to safety before retreating. As the monster weaves through the park, Erin rescues a young girl from a ride, but is swallowed whole in the process. From a walkie-talkie, Erin calls Les, revealing that she is still alive. The trio retreats to a haunted roller coaster where they attempt to rescue Erin.
Inside the ride, Hawk readies a desperate strike, but Unteka flings him aside. With no one else able to stop it, Les sacrifices himself, allowing the snake to consume him in order to draw it away from Erin and Hawk. In a dramatic moment, Unteka lunges toward an already wounded Hawk, but the creature screams in agony and collapses. Les then cuts a hole in the beast’s chest and, with Hawk’s help, pulls out the heart. Erin and Hawk escape the creature’s collapse, cradling Les as they leave the ride.
Months later, Les and Erin are married and expecting their first child, signaling that Les has finally conquered his fear. The fate of the ancient creature remains a reminder of the costs of fear and the redemptive power of courage.
