“Heretic” is a simple but smart thriller about faith, a horror movie of ideas that is as sinister as it is cerebral.

The writers of “A Quiet Place” and writer-directors of “65” keep our focus on two young women, Mormon missionaries in peril, and on the twisted, Satanic figure who imperils them.

Sophie Thatcher (TV’s “Yellowjackets”) and Chloe East (“The Fabelmans” and TV’s “Generation”), filmed in revealing closeups, register innocence and optimism, naivete and rising unease closing in on terror as they figure out — at different times — the depth of difficulties their last door-knock of the evening has brought them to.

And Hugh Grant, all twinkling curiosity, charm and contempt that turns towards menace, puts on a tour de force of understated villainy as that one older gentleman in the curiously shaped, bigger-on-the-inside house on the edge of town who could be their undoing. You almost forget the “forelock” years of romances like “Four Weddings and a Funeral.” This is a career-redefining post-“Paddington” turn that reminds us he was always more than big blue eyes, unruly hair and a stammer.

Sister Barnes (Thatcher) is the more experienced of the two 20ish young women on Schwinns, handing out pamphlets, approaching often curt and dismissive strangers in town in this corner of the Rockies. Sister Paxton is eager to save her first soul by sharing “all the ways God reveals his plan.”

It’s raining and getting dark when they come to Mr. Reed’s house. He’s someone who earlier expressed an interest in learning more about their faith. He charms at the door, expressing delight at their arrival. And when Sister Barnes notes that they can’t come in without a woman present, assures them his “wife” is in the kitchen, finishing up a pie.

They chat as they wait on the wife and the pie, and as the camera closes in, the supposedly unknowing and curious potential convert reveals that he already has a worn copy of The Book of Mormon, filled with notes and page-tags. And his questions become a lot more pointed than much of what the missionaries have heard about that Mormon-bashing “‘Southpark’ musical (“‘The Book of Mormon’).”

He starts with queries about one woman’s dead father and “signs” that she’s felt his presence after his death. They all have thoughts on the afterlife. And then he drops the big one.

“How do you feel about polygamy?” Their response to his “misogynistic practice” and prophet Joseph Smith’s rationale for womanizing is rote Latter Day Saints dogma about the “practicality” of it in a female-dominated (in its early years) faith.

The digging goes deeper as Mr. Reed trots out props to make his points about “iterations” of ritual and belief through the ages, which must — in his mind — point back to what could have been “the One True Faith.” The young women haven’t his years of research or experience of the world, but try to hold their own even as they concede points about this or that Mormon rationalization or reversal of practice and preaching or even that Smith himself was pretty “sketch.”

But where IS that wife? Where is that blueberry pie they’re smelling that she’s making? Why WOULD this guy have all the versions of the board game Monopoly, including the one that pre-dated it by decades and was stolen by the credited inventor, just to make his point?

Why did he make note of the fact that the “walls and ceilings have metal in them. I hope you don’t mind,” as regards the cell phones that won’t work.

One thing’s for sure, as the debate shifts to fast food, his “I’ve never had a Wendy” is a Freudian slip for the ages. The Sisters — first one, then the other — grasp just how much danger they’re in. They must hide their panic, insist again on seeing the wife and reason (in a panic) and work-the-problem their way out of this peril.

“Heretic” leans on horror and serial killer thriller conventions for its plot and rising suspense. The foreshadowing is obvious, but the ways it is deployed always surprise and chill.

Grant’s villain is deeply considered but still only vaguely defined — supernatural menace, or all-too-recognizably human monster?

The second act somewhat pointlessly shifts in point of view as we see the church Elder (Topher Grace) they speak of as “expecting us back” start to fret about their absence and the darker and darker turns in the weather. And the third act’s grim and gruesome violence and “tests” don’t entirely obscure the struggle for clarity as the writers-directors try to wrap things up in a “What it all means” moment.

But this is top drawer horror, a smart movie that dissects faith and belief and religions in search of their purpose as it trots through the tropes of all the ways the world and the creeps in it are a threat to young women, especially the religious ones.

And Grant’s outing joins the ranks of the great horror villains with an erudite and evil turn for the ages, a “Heretic” who cannot be heard or experienced without sending a chill up the spine of the faithful and the faithless alike.

Rating: R, graphic violence

Cast: Hugh Grant, Sophie Thatcher, Chloe East and Topher Grace

Credits: Scripted and directed by Scott Beck and Bryan Woods. An A24 release.

Running time: 1:50