A group of teenagers who are camping in the area come by Harley's store, and the man's son is killed after being hit by one of their dirtbikes. One of the teens, Steve, stays with the injured boy until his father's return, while the rest flee the scene.
At the cabin, the teenagers fight over whether or not they should call the police, until Joel, the one who hit the boy, knocks out one of his friends and locks two of them in the closet to stop them from contacting the authorities.
Harley goes to see a supposed witch, who says she cannot bring his son back, but after Harley relates having seen the creature she controls when he was young agrees to help him seek revenge, but warns him that vengeance comes with a powerful price. On her orders, Harley goes to an old pumpkin patch and digs up a disfigured corpse bringing it back to her cabin, where the witch uses blood from both father and son to resurrect the creature.
Back at the cabin, one of the girls, Maggie, hears a voice whispering her name. Seemingly hypnotized, she follows the voice outside the cabin. Steve brings her out of her trance, but is then attacked by the creature and killed while Harley experiences the murder through the creature's eyes.
The campers go to look for Steve and find only bloody scraps of his clothing. Steve's body then falls from the cabin's roof, and a clawed hand seizes Maggie, dragging her away.
Harley has a vision of the creature killing Maggie and returns to the witch, begging her to stop the monster. She laughs at him and says nothing can stop the monster, and Harley would die too if he tried.
Joel realizes that what's happening is because of him and confronts the monster with a knife, but it swats him aside and drags off another of his friends. The three remaining campers try to get help from the locals, but they refuse, saying the three are "marked". Harley arrives and shoots the creature, but when Joel checks to see if it's dead, it revives and impales him on his own rifle.
A local boy, Bunt, helps the two living campers, Tracey and Chris, reach an abandoned church and relates the legend of the monster "Pumpkinhead" to them, explaining that the creature avenges one who was wronged, but anyone who tries to stop it becomes marked as another victim. The creature attacks and throws Chris against a tree, then drags his body back to Harley's house, where they have taken shelter.
Bunt is caught when Pumpkinhead enters the house; while Harley experiences the murder, the other camper, Tracey, is terrified to see that his face has changed to resemble the monster's. She runs outside and finds Chris injured but not dead, struggling to crawl away as Pumpkinhead prepares to kill Bunt. Harley stumbles out of the barn but is accidentally stabbed in the arm by a pitchfork. Both Harley and Pumpkinhead cry out in pain, and the creature releases Bunt. Harley notices that Pumpkinhead's face is turning more human, then realizes that he and Pumpkinhead are one, and that the only way to kill it is to die himself.
The creature grabs Tracey by the neck, but before it can kill her, Harley shoots himself in the head. Both he and Pumpkinhead collapse to the ground. Harley, however, suddenly awakens, which causes Pumpkinhead to also reawaken, and grab Bunt again. Tracey grabs the gun, with Harley begging her to kill him. Harley, now fully changed, tries to attack Tracey. She shoots him several times until both he and Pumpkinhead fall to the ground, dead. Tracey, Bunt and Chris then watch as Pumpkinhead bursts into flames. Later that night, back in the pumpkin patch, the witch is burying Harley's now disfigured corpse in Pumpkinhead's grave.