We’re in a pretty great period for established actors doing weird shit. Obviously, there’s Nic Cage, playing everything from an ancient vampire to a deranged satanist to an average man who haunts your dreams. But the likes of Amy Adams (mom who transforms into a dog) and Hugh Grant (oompa loompa and evil wizard) are also in experimental eras. Now, Grant has taken perhaps his most surprising role: the antagonist in A24’s horror movie Heretic from codirectors Scott Beck and Bryan Woods. Even more surprising? He’s scary as hell.

Heretic is centered on two young Mormon missionaries — Sister Barnes (Sophie Thatcher) and Sister Paxton (Chloe East) — who aren’t having much luck preaching the good word door-to-door. So, when they meet Mr. Reed (Grant), who is extremely interested in a religious discussion, they let their guard down a little too much. But the bad signs are there: a wife that never seems to appear, a fake blueberry pie baking in the oven. By the time they realize they need to get out of there, it’s obviously too late.

Mr. Reed doesn’t immediately get violent or aggressive. Instead, he turns the tables. After outlining his beliefs — namely that all religion is nonsense, no different than fast food or Monopoly or pop music — he becomes the one trying to convert his new captives. Barnes is defiant, staying true to her beliefs despite Reed dissuading her, while Paxton initially just says whatever she thinks will get her out of the house.

What makes this so scary, before the film’s psychological scares eventually turn gruesome and violent, is Grant himself. Part of the reason he’s played the lead in so many romantic comedies is that he has a very particular bumbling charm. Grant isn’t the perfect, chiseled leading man. He’s awkward and comforting in a way that puts you at ease. As Mr. Reed, this disarming nature turns into a trap.

I won’t spoil too much about what he’s selling, but Mr. Reed is essentially a theological debate bro. He’s extremely well-versed in seemingly all of the world’s religions, and he wants someone to challenge his ideas — not to change his mind but so that he can prove how smart he is by winning the argument. He has spent his life anticipating questions and finding his answers. This pathological need to be right is pushed to its extreme as Heretic moves along; it starts out a little silly and funny but eventually is just terrifying.

And it’s echoed in Mr. Reed’s own home: a warm and cozy front room gives way to an unsettling labyrinth that puts Barbarian to shame. The further into its depths you see, the more fucked up Mr. Reed’s philosophies become. He just can’t be wrong, and he’ll do anything to keep that from happening. Those lengths range from casual murder to singing Radiohead’s “Creep” despite having a terrible voice.

The interesting part of Heretic isn’t its views on religion — which, it seems, boil down to all of them being equally bad, though Reed’s solution turns out to be far worse — but rather how Grant is the ideal vehicle to explore how boring evil can initially seem. He’s a bookish nerd in a cardigan with dogeared copies of The Bible and The Book of Mormon. He offers you pie and drinks when you enter his home. He’s Hugh Grant: he’s not scary at all. But then he suddenly is, driven by the force of his twisted beliefs. And that turn to terror is as scary as any fictional monster.

Heretic hits theaters on November 8th.