A murderer known as the God's Hand Killer has been terrorizing Texas when Matthew McConaughey walks into the local FBI building claiming his brother is the killer. We then flash back to the 70s when MM and his brother were kids living with their widower father, played by Bill Paxton. Bill wakes the boys up one night in a panic and tell them he was visited by an angel (a tiny angel on top of his bowling trophy no less) who told him God has chosen them to kill "demons" disguised as normal people. The younger brother falls for this immediately of course, while the older brother does everything he can to prevent it.
In the end, I have no idea why I didn't like Frailty before, but I'm making up for lost time now. I give Frailty 8 out of 10 fireflies.