“Heretic” begins with an unusual table: two young missionaries from The Church of Jesus Christ of Latter-day Saints They are discussing condoms and why some are labeled large even though they are all more or less a standard size. “What else do we believe thanks to marketing?” one asks the other.

That line will resonate throughout the film, a stimulating discussion of religion that emerges from the packaging of a horror movie. Despite a slide in the second half and feeling unbalanced, this is the rare film that combines a lot of gore and a lofty discussion of the ancient Egyptian god Horus.

The two members of our church, played fiercely by Sophie Thatcher and Chloe East, are wandering around trying to hide souls when they knock on the door of a cute cottage. Its owner, Mr. Reed, offers a cordial “Good afternoon!” He welcomes them, brings them drinks and promises them blueberry pie. He is also interested in learning more about the church. So far, so good.

Mr. Reed is, of course, if you’ve seen the poster, the bad guy and is played by Hugh Grantthat doesn’t go the route of the grumpy, dead-eyed Hannibal Lecter in “Heretic.” Grant is the slightly awkward, shy and mocking character we fell in love with in “Four Weddings and a Funeral,” but with a tinge of menace. He slowly reveals that he actually knows quite a bit about the Mormon religion and about all religions.

“It’s good to be religious,” he says cheerfully and promises that his wife will join them soon, a requirement for the church. Homey touches in her house include a framed embroidery that says “Bless This Mess” on one wall, but there are also oddities, like her lights are on a timer and there is metal on the walls and ceilings.

Writer-directors Scott Beck and Bryan Wood, who also combined on “A quiet place” – have remarkably prepared us for an unexpected theological debate here. Mr. Reed is no different than a serious professor of comparative religion pitted against two naïve missionaries armed with talking points that mask their own doubts.

Mr. Reed knows exactly where the weak points are and sticks the philosophical knife in. “How do you feel about awkward questions?” he asks before addressing the church’s stance on polygamy. “Yeah, it’s a sketch, for sure,” East’s Paxton sister finally admits. Soon the discussion turns to which religions market best. After all, Mr. Reed is up against a couple of walking, talking advertisements for Mormonism.

“Heretic” is so beautifully constructed and performed in the first half that you won’t really notice when it turns into a horror movie. You may be one step ahead of the missionaries, but not by much. Mr. Reed alternates between creepy and funny, and is no stranger to Spider-Man and Voltaire, Radiohead and the Hollies, Wendy’s and Taco Bell. Grant has gloriously weaponized his natural charm.