Fenton Meiks (Matthew McConaughey) visits FBI Agent Wesley Doyle (Powers Boothe) claiming that his brother Adam is the culprit in the “God’s Hand” serial killings. Fenton says Adam has committed suicide, prompting Fenton to fulfill a promise to bury his brother in a public rose garden in their hometown of Thurman. He begins to tell Doyle about the boys’ childhood and suggests that the bodies of the God’s Hand victims are buried in the rose garden. Fenton continues telling Doyle his story as the two drive to Thurman.
In the summer of 1979, when the brothers (Matt O’Leary and Jeremy Sumpter) were children, their father (Bill Paxton) told them that he’d been visited by an angel and tasked by God with destroying demons disguised as human beings. He explained that this mission was now the responsibility of the three of them and must be kept secret from all others. The father’s modus operandi is to wait for the angel to give him a list of names of those who must be destroyed. He then abducts an individual from the list, takes them to the family home and, with his sons present, touches them, which, he says, grants him a vision of the crimes the demon has committed. He then kills the victim with an ax and buries the body in the rose garden.
Adam believes in their father’s mission and says that he sees the same visions of the demons’ crimes that their father sees. Although he goes along out of fear, Fenton doesn’t believe; he is convinced that their father is insane and has brainwashed Adam. Eventually, Fenton tries to stop the crimes by telling Sheriff Smalls (Luke Askew) what has happened. Smalls visits, and Fenton insists that he search their storm cellar. The father ambushes and kills Smalls, and is distraught at having been made to kill someone for what he believes is the first time.
The father blames Fenton for revealing their mission and thus forcing him to kill Smalls. He further implies that the angel has told him something about Fenton he doesn’t want to believe. To cure Fenton’s apparent lack of faith, he locks him in the root cellar hoping Fenton will have a divine revelation. After many days of starvation, Fenton tells his father that he has indeed seen God and is ready to take his place in the mission. Upon the next abduction, Fenton is given the ax to deliver the death blow, but at the last second kills his father instead. As Fenton moves to free the hostage, Adam takes up the ax and kills him first. The two boys bury the bodies in the rose garden. Fenton asks Adam to bury him in the rose garden, too, should Adam ever “destroy” Fenton.
Doyle is puzzled by his phrasing, thinking that Fenton is taking him to bury Adam in the garden, not the other way around. “Fenton” then reveals to Doyle that he is in fact Adam and that he has destroyed the real Fenton, who grew up to become the God’s Hand killer. Flashbacks reveal that Adam did in fact share his father’s visions of those they abducted committing horrific crimes, just as he’d always claimed (whereas Fenton did not; as such, Adam always feared that Fenton was a demon). When Adam touches Doyle, a new vision reveals that Doyle had murdered his own mother. Doyle asks, “How did you know?” and Adam replies that Doyle’s name was given to him on the list of demons to be destroyed. Doyle tries to protect himself by reminding Adam that people at the office saw him, but Adam just declares that God will protect him, then strikes down Doyle with the ax.
Those who saw Adam (posing as Fenton) at the FBI office inexplicably remember nothing about his appearance. In the surveillance tapes, his face is obscured by static. The investigation then proceeds as Adam predicted: FBI agents raid the real Fenton’s home and discover evidence of his crimes, as well as Doyle’s badge, planted by Adam. Agent Griffin Hull (Derk Cheetwood) visits the Enid County Sheriff—Adam Meiks—to deliver the news about Fenton. Hull doesn’t recognize Adam, even though he was one of the people who saw him at the FBI office the night before. Shaking Hull’s hand before he takes his leave, Adam tells him he’s “a good man,” indicating he’s seen that Hull has not committed any crimes. He departs, Adam telling his pregnant wife that “God’s will has been served.”