Hugh Grant, an actor who gained mammoth worldwide fame as a charismatic lead of easily exportable British romcoms, has worked hard off screen to remind us that this really isn’t who he is or ever really wanted to be seen as. He once called himself “a nasty piece of work”, also listing the many female co-stars who ended up loathing him, a reputation supported recently by Jerry Seinfeld and at one point Jon Stewart, who called him the worst guest he’s ever had.

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It has felt rather freeing to see Grant untethered by expectation (last year’s disastrous Oscars red carpet interview saw responses split by location, with some calling him rude and others simply calling him British) and it’s allowed him to take on some lightly darker roles on screen. While he might have played baddies in Paddington 2 and Dungeons & Dragons, there’s still been a roguish PG-mandated charm shining through, a villain who might send his henchmen in but wouldn’t quite twist the knife himself.

In the enthusiastically R-rated horror-thriller Heretic, Grant is very much holding the weapon, although it’s unclear from the outset just what that weapon is and how he’s going to use it. What we do know is that the two Mormon missionaries, who make the mistake of knocking on his door, are in trouble, Sister Barnes (Yellowjackets’ Sophie Thatcher) and Sister Paxton (The Fabelmans’ Chloe East) hoping to convert him on a rainy afternoon. His house is remote but he insists that his wife is inside so no rules will be broken (rules dictate that a woman must be present if they’re alone with a man). Initially, he seems like an ideal candidate, curious and enthusiastic and far more aware of the intricacies of the religion than most. But his need for discussion and debate starts to turn into something darker as he challenges the morality of their doctrines, and, as the girls attempt to leave, they realise that something bigger is planned for them.

What’s such a great surprise, and such a great pleasure, is just how talky Heretic is, the first half akin to watching a juicy stage play, reminiscent of Deathtrap or Sleuth, a sneaky game of psychological cat-and-mouse that’s far more tense because of how withheld the more in-your-face horror is. Grant’s speechifying, crafted by A Quiet Place duo Scott Beck and Bryan Woods, is smug, sure, but also delicious in its provocations, striking at hypocrisies and inconsistencies within religion, like an anti-preacher delivering a hateful sermon. It’s then rather thrilling to see the missionaries gain the strength to strike back, a captivating game of high-stakes tennis that’s far more satisfying than any action sequence I’ve seen this year. Grant tears into it with such ebullient vigour that it feels as if he’s been waiting for something like this for decades, a performance of total freedom and what seems like genuinely giddy pleasure. He gives us flashes of the same disarming charm we associate him with, but here it’s used as part of his weaponry as he tries to cajole his opponents into playing his sadistic game. Disappointingly, the ultimate nature of the game isn’t quite as well-figured out and as the film enters full genre territory, as commanding words get sidelined by unconvincing actions, Heretic stretches our belief.

Grant still keeps us more engaged than we’re used to at this late stage (it’s a considerable step up from hearing, say, Jigsaw do the same) but while hearing him monologue in the outset proved endlessly compelling, it’s less interesting to hear him do this in the last act, spiky theories about religion and human nature turning into confusing and far less intelligent exposition. His performance is of such stature that it threatens to steal the film, yet he’s matched by two crackerjack performances from Thatcher and East, who have us entirely invested in their survival. Thatcher had already proved her genre worth in Yellowjackets and The Boogeyman but East, nailing comic support without turning her character into a buffoon, is a real revelation. The pair keep us caring about just how horrible things may get even when the goofier elements of the writing threaten to push us away.

It’s a fascinating test of patience for many Friday night horror fans, given how long the film takes for anything truly, viscerally nasty to happen, and when it does, it’s nasty enough to jolt us (a moment of bloody digging is almost unwatchably gory). As grim as some of the imagery might get, Beck and Woods are still most focused on ensuring we have a good fun time (this is the rare A24 horror film that isn’t drowning in trauma). Heretic might not be good clean fun but Grant makes it worth us getting dirty.