“Frailty” is a creepy little misfire of a movie about a serial killer who says he’s getting instructions from God. Its clunky, screenwriterly script gets by on two inventions. One is a “Twilight Zone” ending. The other is a murderous father who commits these crimes in front of his two small boys, as a way of getting them right with God.

Appropriately set in Texas, the movie clumsily begins in the present as a man tells an FBI agent the solution to a long-unsolved crime.

Fenton Meiks, played by Matthew McConaughey, says that a current string of murders is tied to killings committed by his father in the late 1970s. The incredulous FBI guy, played by Powers Boothe, listens as Fenton tells how his mechanic father (Bill Paxton) began seeing visions on bowling trophies, on the oil pans of cars he was working on.

“We are God’s servants,” he told his 10- and 8-year-old sons, Fenton and Adam. Their mission? To kill.

As the crimes begin, Fenton resists his father’s urging to take up the call. Their battle of wills is the most interesting thing about the movie, and it is well-acted by Matthew O’Leary, who ably plays the young Fenton. He and his father struggle for the soul of the impressionable younger son, Adam (Jeremy Sumpter). Adam likes dad’s “superhero” take on their mission and their three “holy weapons,” given to them by an angel. Fenton says that there is no God, and Dad’s crazy.

This would be an authentically disturbing take on religious lunacy on the order of “The Rapture” if it weren’t for laughably amateur construction and dialogue by first-time screenwriter Brent Hanley.

Too many scenes switch from the present to the past with an, “It was later on that same night,” a trite Screenwriting 101 misunderstanding of the way memory works.

But the kids are great, and this plot could certainly be the foundation of a much better thriller.