Wesley Doyle (Powers Boothe), the FBI agent heading the search for Texas' notorious "God's Hand" murderer, is understandably suspicious when a man walks into his office and announces that he knows the identity of the elusive serial killer. Introducing himself as Fenton Meiks (Matthew McConaughey), he claims that his brother, Adam, killed all those people and then killed himself. But Adam's crimes are just one small part of a long and complex story that Meiks wants to share with Doyle so he will understand what motivated his brother to kill. Past and present converge as the two strangers drive together to the rose garden where Adam is buried and Meiks begins his tale of faith and retribution.

It is 1979 and the Meiks brothers, twelve-year-old Fenton (Matthew O'Leary) and nine-year-old Adam (Jeremy Sumpter), enjoy an idyllic relationship with their father (Bill Paxton), a kind and sensitive man still recovering from the death of his beloved wife. The boys are happy and secure, until a sudden and inexplicable turn of events changes their lives forever. Dad announces that he has been visited by an Angel who has entrusted him with a holy mission. God has chosen him and his sons to destroy "demons" who pose as ordinary men and women. The Angel will provide them with a list of names. The Meiks must find these "demons" and kill them.

While young Adam is enthusiastic about the family mission and claims to share his Dad's visions of divine justice, Fenton fears that their father is insane. Torn between his love for his family and his belief that their diabolical plan must be stopped, Fenton wrestles with his own demons, searching for a solution. The terrible violence that shatters the brothers' childhood has a dramatic impact on their futures. Deeply affected by their experiences, Fenton and Adam develop extreme ideas about good and evil, ideas that lead them to shocking and unforeseen fates.