Trying to up their "conversion" numbers, two young Mormon missionaries - hard-edged Sister Barnes (Sophie Thatcher) and slightly naïve Sister Paxton (Chloe East) - end up on the doorstep of reclusive Mr Reed's (Hugh Grant) isolated home.
It's pouring with rain and so Mr Reed invites them in, assuring the young women that his wife is in the other room and will be out shortly.
As the missionaries try to engage Reed in the benefits of Mormonism, he throws them a curveball, revealing his knowledge of world religions and starts to challenge their convictions.
What begins as intellectual, philosophical sparring soon ratchets up a gear when Sister Barnes and Sister Paxton realise they are locked in Reed's peculiar house and that the only exit appears to be out the rear of his property.
The increasingly sinister Mr Reed, talking about his discovery of the "one true religion", presents them with a choice of two doors: one marked Belief and one Disbelief.
Distributed by A24,
Heretic is an incredible film, resting as it does largely on the shoulders of its three stars.
Giving a disturbing, tour-de-force, award-worthy performance Hugh Grant demonstrates how he has morphed into playing the most incredible bad guys in recent years while still drawing on his legendary, natural, charm.
However, standing up to his strength of personality, both Chloe East and Sophie Thatcher shine as the two women of great faith and mental fortitude.
The volume of intellectual repartee sometimes gives Heretic a play-like ambience, but the incredible tension generated by the exchanges between the main characters never lets you forget that you're watching a horror movie and that anything could happen at any moment.
Although the film runs for almost two hours, the tension and pacing ensures that once you are intellectually immersed in this world, time flies by.
Be warned, depending on your genre expectations, this is not a pulpy slasher flick, more a psychological powder keg ready to figuratively explode in unexpected - and mysterious - ways.
Written and directed by Scott Beck and Bryan Woods, Heretic is trying something different with the genre and - for the most part - this works really well if you let it.
The movie is almost a "think piece", designed to stimulate conversation about the topics raised (such as the iterations and roots of organised religion, the nature of belief etc) rather than the quality and goriness of any particular kills.
As with all the best horror films - and this is one such beast - the less you know about the plot going in the better.
Also, as with a great many horror films (where such an act is often the hardest to pull off), I'm not entirely sure that Heretic sticks the landing, but it certainly hammers home its message in no uncertain terms.
While not always particularly subtle, I'm sure there are layers, symbolism and metaphors in this work that I missed.
To that end, Heretic is definitely a film I can see myself not only revisiting but recommending to others wholeheartedly to hear their thoughts and opinions.
