Bill Paxton, who died unexpectedly Saturday at the age of 61, will always be fondly remembered as a film and television star—one of James Cameron’s favorite actors, a fixture of some of the most beloved movies of the past fifty years. But for fans of Paxton’s 2001 directorial debut Frailty—of which there are many—Paxton wasn’t just an accomplished character actor. He was also a bona fide auteur.

Frailty is a project of staggering audacity. If Paxton had gotten pretty much anything wrong, this tonally tricky film would be remembered as a cult classic for all the wrong reasons. After all, it’s the story of a nice, responsible dad telling his children that God wants them to murder demons disguised as human beings. Yet Frailty purposefully eschews camp—and comedy altogether—in favor of a seriousness that marks it as a film of rare commitment and conviction.

Paxton’s debut unfolds with the spooky atmosphere of a campfire ghost story. It begins with Matthew McConaughey, in one of his best mid-period roles, telling an FBI agent (played by the great Powers Boothe) a different kind of spooky tale, one involving his own father (Paxton). In flashbacks, Paxton’s character tells his two sons that he has received a vision from God, ordering them to “destroy” demons disguised as human beings. As family projects go, this one’s a little darker than most, and his older son is understandably reluctant to kill people on his old man’s behalf.

In a beautifully modulated performance, Paxton plays this father not as a psychopath, but as a man of absolute moral certainty—a zealot who has no choice but to follow the path laid out for him, no matter how insane or evil it might seem. He labors under the delusion that he’s not only moral, but an instrument of ultimate morality. Paxton’s performance goes a long way towards grounding lurid paperback subject matter in concrete, recognizable reality.

As a filmmaker and an actor, Paxton never winks to the audience. He never lets them in on the joke—because there is no joke in Frailty. There’s no distance, no irony—just the furious conviction of an actor who believes in the reality of his situation to such an extent that he’s able to make the audience believe it as well. Paxton never loses that core of paternalistic decency, even when he’s dismembering the wicked with an axe. And in treating this pulpy subject matter with absolute, ferocious sincerity, Frailty elevates it to the realm of southern gothic or the Old Testament. Paxton made a movie about religious zealotry that takes that zealotry seriously.