There will no doubt be some people who saw the trailer for Heretic and thought, "People being held against their will? I've seen that a hundred times now," but that's just the thin wrapping paper that covers this intricate puzzle box.
Enormous credit goes to the writers who played such a big part in making this film so refreshing. Rare is it that characters, who would be easy to be two dimensional, in a premise like this feel so human. From the way the discussions the missionaries have together, to the intricate details the viewer may have thought were ignored, it's all covered so well. Sophie Thatcher and Chloe East are excellent in their roles, being friends who outside of their faith, may not have forged a relationship at all, with their respective cynicism and naivety both being fleshed out. Unsurprisingly, Hugh Grant steals the show with his brilliant performance as a rational thinker who goes to irrational lengths. He's so disarming and so... Hugh Grant, that there are numerous times one can't help but smile, even as things take a turn for the worse, demonstrating how everyday monsters use their charm to do terrible things.
It also makes a nice change to feel genuinely tense and worried for the characters, instead of because you're expecting a jump scare. The atmosphere is superbly woven and its clever intricacies leave the viewer constantly wondering what's to come.