Many great horror movies deal with families; that is where we are all most sensitive. This uneven film exploits that vulnerability but is ultimately unsatisfying.

The film opens on a dark and stormy night; Fenton Meiks, (Matthew McConaughey) a troubled-looking young man, has walked into the Texas offices of the FBI. He claims to know the identity of a serial killer, known as “God’s Hands” and he wants to tell his story.

As the story unfolds in flashback, Fenton describes growing up with his widower father (Bill Paxton) and younger brother Adam. It’s a generally happy household; Fenton and Adam are close, and kind to one another, and their father clearly cares for them both. Bill Paxton’s Dad character is convincing as a working-class guy with enough love and discipline to bring up his two boys alone, which makes his subsequent transformation very disturbing.

One night, he gets the boys out of bed to declare that an angel has brought him a vision. They’re living in the End Times, and God has selected the family for a special mission, to seek out and destroy demons, who are moving among humans in the last days. The demons look like ordinary humans, but Dad knows the difference — he says that he receives their names from heaven, and can see their sins at the moment he dispatches them by touching them with his hands. He uses a divinely selected ax and a lead pipe to perform the actual “destruction” of the demons.

Adam, the younger and more pious of the brothers, believes what his father tells him and immediately throws himself into the role of divinely appointed avenger. Fenton, older, keeps his doubts secret until his father actually drags home a bound woman and then executes her in front of his children.

Fenton is horrified, but forced to take an increasingly active role in the “demon” hunting. His initial rebellion against the new family business is handled by his father firmly, but lovingly. His dad has no doubts but realizes how difficult it is for his son to accept his new role in the universe. Nevertheless, as Fenton resists more and more, his father takes increasingly stern action, eventually locking his son in the cellar, to pray for a vision.

The genuinely horrifying premise of this film is undercut by its ham-handed writing, which makes the plot even less plausible. The dialogue is full of wooden homilies like “The truth is pretty unbelievable sometimes,” which Matthew McConaughey’s character drawls just before spilling the beans to the FBI. The dialogue is unintentionally funny at a number of points, especially when Bill Paxton is carefully delivering exposition on his insane plot. What is supposed to be a chilling matter-of-fact tone sounds more like a cold reading of the script.

This is not to say that the film is not frightening. The “destructions” are horrifying. The fact that we do not see the worst leaves the graphic details up to our imaginations. The scenes of Fenton locked in the cellar are extremely harrowing. But the most disturbing aspect of the plot is that the murders take place in front of the young sons, and committed by a beloved father. As Alfred Hitchcock said of the death of a child in an early film of his, “It was an abuse of cinematic power.” For a film as empty as “Frailty,” there is simply no excuse.

Many children will be disturbed by the spectacle of a loving father going crazy and becoming a homicidal maniac, and the consequences for the family. There are a number of shocking and tense moments among all the schlock.

Families seeing this film will want to discuss both Adam and Fenton’s reaction to their father’s revelations. What would you do if your father or mother told you they were commanded by God to kill the guilty? An especially troubling aspect of the movie implies that the father’s visions are real, and that God has actually selected a number of people to kill specific evildoers with an ax. Families of any faith will want to discuss the difference between the movie’s depiction and real-world religion.

Families who enjoyed this film will want to see “Psycho”, “The Brood,” “Carrie” and “Unbreakable”, four excellent films with similar themes.