The psychological thriller "Frailty" marks the directorial debut of actor Bill Paxton and comes garlanded with praise from the likes of Stephen King, James Cameron, and Sam Raimi. Does it deserve their plaudits? In a word, yes.

"Frailty" is gripping, thought-provoking and disturbing. What makes it so is, above all, Paxton's fearless performance in the movie's pivotal role.

Paxton plays a working-class widowed father who's raising his two young sons by himself. The family's life is perfectly ordinary until, one day, Dad tells his sons that God has chosen him to destroy "demons" posing as ordinary men and women.

Nine-year-old Adam (Sumpter) idolises his father and embraces his mission with enthusiasm. Three years older and wiser, Fenton (O'Leary) is aghast.

Although he believes his father is mad, he is powerless to prevent him from going through with his grisly task.

The story of Fenton's appalling dilemma is related in flashback. Some 20 years later, a man (McConaughey) walks into a Texas police station, introduces himself to FBI agent Wesley Doyle (Boothe) as Fenton Meiks and declares that he knows the identity of a serial killer at large in the state...

"Frailty" could so easily be ludicrous, but Paxton doesn't flinch from the challenge - either behind or in front of the camera.

As a director, he is resolutely old-fashioned. For all the movie's horror, there is very little gore and certainly none of the knowing, camp irony of the "Scream" films and their post-modern ilk.

As an actor, meanwhile, he conveys his character's insane conviction but never entirely loses our sympathy.

A movie exploring the dangers of fanaticism is all too timely in today's world. But "Frailty" goes a stage further, mixing simple polarities of good and evil with a series of unexpected plot turns.

The twists ultimately make the film morally ambiguous - and all the more terrifying for it.