Plot
In his office in Dallas, FBI Agent Wesley Doyle is visited by Fenton Meiks, who says his brother Adam is the culprit in the "God's Hand" serial killings that Doyle is investigating. Fenton says that Adam has committed suicide, prompting Fenton to fulfill a promise to bury his brother in a public rose garden in their hometown of Thurman, Texas. Doyle is initially skeptical of Fenton's claims, but when he calls the Thurman Sheriff's office, a deputy confirms that Fenton did steal an ambulance and his brother's body earlier that day. Fenton begins to tell Doyle about his childhood, and suggests that more bodies of the God's Hand victims are buried in Thurman's rose garden.
In the summer of 1979, Fenton and Adam lived with their father, a local mechanic and a widower, in the groundskeeper's cottage just behind the rose garden. One night their father explained to them that he had been visited by an angel, and that their family had been tasked by God with "destroying" demons disguised as humans on Earth, a mission which must be kept secret. Fenton is confused and frightened by their father's story, while the younger Adam seems to take the information as received. Their father is soon led by more visions to discover three holy weapons: an axe carved with the name "Otis", a pair of work gloves, and a section of pipe. Eventually, he also claims to receive a list of names from the angel of people whom he now believes to be demons.
Fenton goes on to explain that their father incapacitated his first victim, a woman named Cynthia Harbridge, with the heavy pipe, before then bringing her back to their family home. When he removes the gloves and lays his hand on Cynthia, his father claims to see visions of her evil, while the "demon" also seems somehow further weakened by their evil being revealed. Their father then kills Cynthia with the axe and makes the boys help him bury her body in the rose garden. Horrified, Fenton believes his father has gone insane, but Adam now claims to also see their father's visions and supports their mission.
After telling him this story, Fenton is handcuffed by Doyle and placed in the back of a car while he drives them both to Thurman. On the way, Doyle reveals that his own mother had been murdered by someone who was never caught. Fenton then explains how his father enlisted his help to trick and abduct their second victim, Edward March, from a grocery store parking lot in broad daylight, with his father insisting that God would blind any witnesses. They take March back to their home, where their father murders him with the axe in their backyard shed.
Fenton's mental condition deteriorates from the shock and stress of his father's killings. One night, his father tells him he prayed for the angel to visit Fenton and alleviate his lack of faith with visions of his own, but the angel instead visited him again and told him something terrible about Fenton that he chose not to believe. He then makes Fenton dig a large hole in the backyard, seemingly to test his will and help bring him to faith. While digging for entire days on end, Fenton refuses to wear work gloves, and he eventually completes the hole while resolving to abandon all faith in his father's God. Their father then builds the hole into a cellar, and he moves the shed directly on top of it.
During his father's third abduction of an unspecified man, Fenton runs from the cellar to find the local sheriff, who proves skeptical of Fenton's story and takes him back home. Noticing Fenton's genuine-seeming fear, the sheriff asks his father to take a look in the cellar, which he then finds empty, as Fenton insists that the victim must be somewhere nearby with Adam. The sheriff no longer seems interested in Fenton's wild stories and turns to leave before their father also kills him with the axe.
Their father is grief-stricken over having killed an innocent man, and is angry with Fenton for forcing him to commit murder to protect their secret mission. After burying the sheriff's body in the garden, Fenton's father reveals the angel had told him that Fenton is in fact a demon. To save his son and encourage his faith, he locks Fenton in the cellar for more than a week with almost no food, and only a cup of water per day brought to him by Adam. Fenton eventually suffers a mental breakdown, and he finally claims to have been enlightened by his own vision of god. His father releases Fenton and embraces him now that he's ready to help carry out their next killing.
Fenton cooperates with his father to take the next victim, Brad White, but he accidentally alerts him just before his father can hit Brad with the pipe. Their father is injured in the ensuing fight, but with Fenton's help they are able to knock him unconscious. In the cellar, his father gives Otis to Fenton and commands him to destroy the demon. Fenton raises the axe to strike Brad, but then hits his father in the chest instead, killing him. Adam rushes to their father's side, and in his dying moments, their father whispers something to Adam. Fenton then tries to release Brad, but Adam instead kills Brad with the axe. The boys bury the two men in the rose garden, and Fenton makes Adam promise to bury him in the garden if Adam ever "destroys" him.
Having now arrived at the Thurman rose garden in the present, Doyle is puzzled by Fenton's phrasing of the story, since Fenton had previously told him that Adam killed himself. The adult "Fenton" then reveals that he is actually his brother Adam. Fenton, possibly seeking to stop others who had received visions like his father's (or possibly simply having gone insane), had grown up to become the actual God's Hand serial killer, and was responsible for several murders that were unrelated to Adam and their father "destroying demons." Doyle is horrified to see the number of graves in the garden.
Adam further reveals that he really did share his father's visions, and that all of their victims were genuinely guilty of terrible crimes. Adam then lays his hands on Doyle and confirms that Doyle was the one who murdered his own mother. Doyle is incapacitated by the revelation, and as he is placed in an open grave he asks how Adam knew. Adam tells him that he was on his list, as he has continued their father's work for all the ensuing years. Doyle says that people will come looking for him because he is an FBI agent, but Adam remains confident that God will protect him. He then kills Doyle with Otis and buries him in the rose garden.
After Doyle's disappearance, Agent Griffin Hull, who had previously met Adam in person in Dallas, can no longer seem to remember face. All of the security tapes from the Dallas FBI office are also inexplicably obscured by static whenever Adam is in view. The FBI raids Fenton's house, finding the God's Hand list with Doyle's name on it, and "trophies" from Fenton's victims, including Doyle's badge, buried in the basement, implicating him as the killer.
Later, Agent Hull visits Adam, who is revealed to now be the sheriff of Thurman, to inform him that Fenton was the God's Hand killer. Hull still does not seem to recognize Adam, and upon shaking his hand and not seeing any visions, Adam tells Hull that he is a good man. As Agent Hull leaves, Adam's pregnant wife (who is revealed to be the same deputy who initially corroborated Adam's story to Doyle over the phone) asks if everything is okay. Adam tells her that everything is fine and that God's will has been done.
