Scott Haze’s riveting performance is at the heart of “Child of God.” (Well Go USA Entertainment/Well Go USA Entertainment)

“He was of German and Irish bloods . His name was Lester Ballard — a child of God, much like yourself, perhaps.” These words, spoken in somber voice-over by the actor Tim Blake Nelson — in the guise of a man with the telling name of Sheriff Fate — open “Child of God,” a spare and unsparingly horrific portrait of depravity.

Adapted from Cormac McCarthy’s 1973 novel by the filmmaker and actor James Franco (who co-wrote the screenplay with Vince Jolivette), “Child of God” is shot without bells and whistles. Like McCarthy’s prose, Franco’s hand-held camerawork draws the story forward as unfussily as a shepherd leads a sheep, and yet with a kind of ghastly grandeur. This is functional filmmaking more than it is flashy.

But there is, at its heart, a single virtuosic performance.

As Lester, an angry, violent homeless man who may be borderline developmentally disabled, mad, or both, Scott Haze is both riveting and revolting. Named by Variety as one of the magazine’s 10 “Actors to Watch” last year, Haze first appears on screen glowering like Malcolm McDowell on the poster for “A Clockwork Orange” as an auctioneer prepares the sell the house Lester grew up in. In his second scene, he’s shown defecating in the woods, like a wild animal.

That is, deep down, what Lester is. McCarthy is said to have based the character on the serial killer Ed Gein, who inspired fictional characters from “Psycho’s” Norman Bates to Buffalo Bill in “The Silence of the Lambs.” In “Child of God,” which is set in Tennessee in the 1960s, Lester begins as the ranting village idiot whom everyone avoids but tolerates, rapidly deteriorating until he becomes a murderous necrophiliac who keeps his rotting female victims in a cave, where he ultimately dresses up in their clothing and scalped hair.

Yes, it’s nauseating. And the film ends without the sort of satisfying moral closure that Hollywood films have conditioned us to expect.

At the same time, Franco keeps you in your seat, mainly by harnessing the power of Haze, whom the director met at a Los Angeles acting school. (Haze has also appeared in Franco’s “As I Lay Dying,” and will have parts in the filmmaker’s forthcoming “Bukowski” and “The Sound and the Fury.”) The actor is mesmerizing here, even though his Lester is often, at best, unintelligible, and, at worst, repellent.

Some commentators have remarked on Haze’s ability to evoke compassion for a character who is a monster, but I’m not sure that “compassion” or “monster” are even the right words. Lester is, in fact, a child of God — i.e., a man — but it isn’t sympathy that we feel for him. Much of the time, it’s something closer to incomprehension or outright revulsion.

Haze does, nevertheless, engender a kind of recognition. It’s not of our common humanity; Haze’s performance is too primal, too stripped away to be relatable on that level. It’s an identification with something that isn’t so much human as bestial.

★ ★ ★

R. At the Angelika Pop-Up at Union Market. Contains violence, nudity, sex and obscenity.
104 minutes.