It begins at a quiet gas station, where a slack-jawed attendant finds himself under attack by a rabid creature, sending his body into grotesque contortions. Meanwhile, a young couple, Seth Belzer and Polly Watt, set off for what they hope will be a romantic camping adventure in the heart of Oklahoma's forests. However, their idyllic plans are abruptly interrupted when they fall victim to a car-jacking by an escaped convict, Dennis Farell, and his drug-addled girlfriend, Lacey Belisle.
As they travel, misfortune strikes when they run over an infected animal on the road, leading to a flat tire. Seeking refuge, the group arrives at the now-deserted gas station. Shortly after, Lacey stumbles upon the horrifically infected attendant writhing in distress in the bathroom. An attack ensues, resulting in her grisly demise, but rather than rest in peace, her corpse reanimates and becomes a new menace, threatening the remaining survivors.
In a frantic struggle to fend off Lacey, Seth, Polly, and Dennis make a chilling discovery: severed remnants of infected victims exhibit a life of their own. When Sheriff Terry Frankel tries to apprehend Dennis, tragedy strikes as he is brutally torn in half by Lacey's reanimated body. The chaos escalates when the creature merges with the upper half of the sheriff, transforming into an even more formidable threat.
Finding temporary safety in the walk-in refrigerator, the trio faces further horror as a piece of the creature's severed arm attacks them—a grim indication of the relentless nature of the infection. It’s revealed that Dennis has also been infected following an encounter with the splintered beast on the road. In a desperate attempt to contain the spread, Seth and Polly perform an amputation on Dennis's arm.
Through their harrowing experiences, Seth learns that the creatures are actually fungal parasites controlling the reanimated corpses and instinctively hunting the living based on their body heat. To devise a plan, Seth cools his body temperature with ice to slip past the creature towards the police car parked outside, while Polly and Dennis create a diversion with fireworks.
Unfortunately, the pursuit ends as Seth discovers that without the keys, the police car and radio are rendered useless. In a desperate and selfless act, Dennis chooses to lure the creature away, allowing for Seth’s escape. As the terrifying creature infiltrates the gas station, the situation grows dire yet again. Hidden in the freezer, Dennis and Polly narrowly avoid the creature's wrath.
The chaos reaches a climax as the discarded fireworks ignite a trail of flammable liquid, resulting in the gas station going up in flames. Armed with a shotgun retrieved from the police car, Seth helps Polly and Dennis escape. In a moment of heroism, Dennis decides to hold back the creature, ultimately succumbing to the infection. In his final moments, he bequeaths Seth a key to a bank account, urging him to assist the widow of a man he had previously shot.
In a grim yet calculated maneuver, Dennis detonates propane tanks, sacrificing himself along with the gas station and any remaining infected corpses. As Seth and Polly make their escape, the haunting final shot reveals that other dormant infected creatures lie in wait within the woods, hinting at a far larger threat yet to come.
