While driving through Mississippi, Caroline and Eli MacCleary get stuck on a deserted road. Eli walks to a service station for help. A creature chained in a cellar breaks free and escapes into the forest. It finds the MacClearys’ car and rapes Caroline. Eli and the service station attendant find her lying in the forest. As they drive off, two gunshots are heard.
Seventeen years later, their son Michael, conceived as a result of Caroline’s rape, has become ill. The family returns to Mississippi looking for information about the man who assaulted Caroline, in case Michael’s illness is genetic.
They learn about the unsolved murder of a mortician named Lionel Curwin, seventeen years prior. The townspeople, including Judge Curwin and newspaper editor Edwin Curwin, refuse to tell them anything. Eli and Caroline ask Sheriff Bill Poole about Lionel’s death. Poole tells them Lionel’s corpse was found partially eaten.
Seemingly possessed, Michael murders and cannibalizes Edwin Curwin. He stumbles to the home of Amanda Platt and collapses. Amanda calls the police, and Michael is taken to the hospital. Doc Schoonmaker tells Michael’s parents that he needs rest.
Michael goes to Amanda’s house to thank her. They go for a walk in the forest. Amanda tells Michael she is the daughter of Horace Platt, an abusive alcoholic who is Lionel Curwin’s cousin. As the teens kiss, Amanda’s dog arrives with Edwin’s severed arm. They alert the sheriff. Horace arrives and commands Michael to stay away from Amanda.
Caroline and Michael return to the hospital, while Eli, Poole, and Schoonmaker search for clues. They uncover a swamp full of human bones with human tooth marks. Schoonmaker thinks one bone belonged to a patient of his who died years ago. The men go to the mortuary and question Dexter Ward, who was Lionel Curwin’s apprentice when the woman died. Ward denies that anyone else was buried in her place. After the men leave, Ward calls the judge and demands money in return for silence. He is soon killed by a possessed Michael.
At the graveyard, the men discover the woman’s coffin is filled with rocks. They return to the mortuary to question Ward but find him dead. Michael, still possessed, finds a man named Tom Laws. Laws converses with the spirit possessing Michael, whom he calls Billy Connors. Assuming direct control of Michael, Connors describes using magic to return as a spirit to punish the Curwin family after his death seventeen years earlier.
The next day, the judge tells Poole to investigate the murders. Laws tries to tell Poole that Connors has possessed Michael and is killing people, but Poole dismisses him. Connors kills Laws for talking to Poole. Afraid of his behavior, Michael goes to Amanda and warns her to leave town. While she packs, Connors and Michael struggle to control Michael’s body. Michael throws himself from Amanda’s window to prevent Connors from killing her. He returns to the hospital and begs to be killed, fearing that Connors will take over and Michael will be unable to stop him. He tells Poole and Eli to go to Lionel Curwin’s house and look in the basement. They find a skeleton with a chain wrapped around its leg, which they assume is Connors’s remains.
At the hospital, Poole, Eli, Caroline, and Schoonmaker witness Michael metamorphoses into a monster as Connors takes control and kills Horace. Everyone flees to the police station. Judge Curwin confesses that Lionel was responsible for Connors’s death. After discovering Connors was having an affair with his wife, Lionel killed her and imprisoned Connors in his cellar. He fed Connors corpses stolen from the mortuary until one night, Connors metamorphosed into a monster, broke free, and killed Lionel. He raped Caroline in the woods before being shot by Lionel’s relatives, apparently returning to the cellar to die.
Connors attacks the police station, kills the judge, and is pursued into the forest. He finds Amanda in a broken-down car and rapes her. When Caroline and Eli find him, he attacks Eli, forcing Caroline to shoot him in the head. It is implied that Connors may have impregnated Amanda, continuing the cycle of his resurrection.