“The serpent will purify you. The serpent will cleanse you.” – The words of a so-called preacher as he drapes a poisonous snake around a young woman who is pregnant in “Them That Follow.”

Here is a monster movie where the monsters are parents.

Parents who won’t hesitate to jeopardize their own offspring’s lives in the name of God — or more accurately, in the name of their insane, cultish, at times literally criminal devotion to THEIR idea of God.

Your faith is your faith, and no matter how bizarre it might seem to outsiders, you should be free to practice that faith without interference.

Them That Follow: 3.5 out of 4 CST_ CST_ CST_ CST_ CST_ CST_ CST_ CST_ 1091 Media presents a film written and directed by Britt Poulton and Dan Madison Savage. Rated R (for some disturbing violence). Running time: 98 minutes. Opens Friday at local theaters.

Unless your faith involves rituals and beliefs that could seriously injure or even kill someone. Psychotic behavior cloaked in religion is …

Psychotic behavior.

Co-written and co-directed by Britt Poulton and Dan Madison Savage, “Them That Follow” is a harrowing and chilling deep dive into an isolated community in the Appalachian mountains, where an evangelical religious sect is so cut off (by design) from the rest of the world, they might as well be living in another century.

Or on another planet.

The terrific Walton Goggins, who is so good at playing intense, wild-eyed, dangerously single-minded characters, delivers memorably intense work as Lemuel Childs, the town’s pastor and unquestioned leader.

Even when Lemuel is sitting in his living room chair, almost blending in with the dark of night, and speaking in quiet and measured tones, it feels as if he’s in your face, screaming at you and rattling your very core.

Lemuel and just about every person in his flock firmly believe in ritualistic snake-handling, which is a real thing dating back to the early 20th century and has been practiced in some churches tucked in Appalachia and pockets of the South.

Snake handling is exactly what it sounds like: You handle an actual poisonous serpent, which embodies sin and evil and the devil himself, and you allow the snake to be draped around your neck — and if you’re bitten, your faith in God should be strong enough for you to overcome the venom without any kind of medical assistance.

Alice Englert plays Lemuel’s daughter, Mara, who is soon to be married. (Fine work by Englert, although she lets her guard down and slips into her native Australian accent a few times.) Mara is betrothed to the deeply religious and upstanding but tightly wound and a little offbeat Garret (Lewis Pullman), who can scarcely believe he’ll soon be wed to Mara and will become a member of the pastor’s family.

Mara doesn’t love Garret. Mara’s heart belongs to Augie (Thomas Mann), but their romance has been kept secret because Augie has stopped going to church and has succumbed to the temptations of the devil, and there’s no way Lemuel would ever allow his daughter to be with this sinner. If Mara even told her father about her feelings for Augie, he would almost certainly disown her and she would be shunned by the only community she has ever known.

But secrets are hard to keep, especially in tightly knit communities where everyone knows everyone, and the romantic triangle in “Them That Follow” eventually becomes the tinderbox that ignites a series of life-changing and sometimes horrifying developments.

The outstanding supporting cast includes Kaitlyn Dever from “Booksmart” as Mara’s best friend and the great Olivia Colman and Jim Gaffigan as Augie’s parents, who are fanatically loyal to the pastor to the point where they’re willing to stand by and do nothing as their son suffers greatly, because Augie’s faith in God should be strong enough to save him.

(The pairing of Gaffigan and Oscar winner Colman might seem unlikely, given Gaffigan is best known for his comedy — but he has proven to be a bona fide dramatic actor in a number of films.)

Colman’s character is named Hope Slaughter. The pastor’s last name is Childs. The indecisive best friend is Dilly, as in in “dilly-dally.” Even the names of the characters in “Them That Follow” carry symbolic weight.

Directors Poulton and Savage and cinematographer Brett Jutkiewicz consistently deliver visually arresting shots, while the music by Garth Stevenson helps build the suspense. In the tradition of such films as “Deliverance” and “Sling Blade” and “Winter’s Bone,” this is a movie where strange and sometimes horrifying things transpire in a part of America we can’t see from the highway.