Here is an utterly absorbing and accomplished debut feature from writer-director Daniel Kokotajlo, known before this for his well-regarded short films Myra and The Mess Hall of an Online Warrior. Apostasy combines subtlety and sensitivity with real emotional power. It also packs a sledgehammer narrative punch two-thirds in, after which life in the film carries on with eerie quietness as usual, while we, the audience, have no choice but to go into a state of shock. It shows that Kokotajlo can really do something so many new British film-makers can’t or won’t: tell a story.

The film is set among a community of Jehovah’s Witnesses in Oldham in north-west England. Kokotajlo grew up in a Jehovah’s Witness family before leaving the faith while at college, and his writing – detached but calmly observant and sympathetic – is evidently based on a real knowledge of this culture, invisible to outsiders. He has apparently used the JW meeting hall in Oldham for the film: the building’s exterior, at any rate. I have to say that Apostasy exposes the slightly preposterous drama of Richard Eyre’s new film The Children Act, with a similar plotline about Jehovah’s Witnesses, based on the Ian McEwan novel. Apostasy is more knowledgeable, less excitable.

Siobhan Finneran plays Ivanna, a middle-aged woman firmly in the Jehovah’s Witness faith: a world in which failure to believe, or to avoid unbelievers, can get you shunned or “disfellowshipped”. She has two teenage daughters: the older Luisa (Sacha Parkinson) is at college and the younger Alex (Molly Wright) is still in school. Both live at home, of course. As to the girls’ father, Kokotajlo leaves that as the great unmentioned subject: whether alive or dead, his past behaviour and current absence is a potent, silent countercurrent to the drama.

Ivanna is concerned about the bad influences Luisa will encounter at college: people of no faith or, even worse, the wrong faith. (She dismisses Catholicism as “wishy-washy”.) Her fears are well founded. Luisa has an unbelieving boyfriend by whom she has got pregnant and her excommunication (to borrow the wishy-washy term) is inevitable. Meanwhile, delicate, shy, clever Alex is very flattered when a young man, an up-and-coming elder in the JW faith, introduces himself to her and her mother at the weekly meeting and asks them both to supper: this is Steven, played by Robert Emms. Alex sees perfectly well how the match is being made by her mother, in concert with the church, so that she will not go down the same route as her sister, and, concerned as she is for Luisa, this responsibility cements her already deeply committed attachment to the orthodoxy. Family tensions become unbearable.

Facebook Twitter Pinterest Siobhan Finneran as Ivanna.

The performances of Finneran, Wright and Parkinson are tremendous and all the more moving for their restraint. Kokotajlo’s direction is lucid and direct. With cinematographer Adam Scarth (who also shot the recent Daphne), he conjures an undramatic world of cloudy days and dull workplaces, kitchens, front rooms. The women’s faces are captured mostly in intimate closeup. Parkinson’s simmering anger as Luisa is almost unwatchably painful, because her rebellion is always tempered by a need not to upset her mother; Wright’s gentleness and tenderness in the role of Alex is heartbreaking.

Finneran’s Ivanna is the most mysterious of all. She is a world away from, say, Geraldine McEwan’s religious matriarch in the BBC TV adaptation of Jeanette Winterson’s Oranges Are Not the Only Fruit in 1989. There is no righteous hysteria, no rage, just an utterly serene contentment with the worldview she has grown up with, and the inevitability of the “new system” that will come into being after this current world has come to an end. But Ivanna’s faith is severely tested, and there is a brilliant scene in which Kokotajlo comes in for another key closeup on Ivanna undergoing a silent dark moment of the soul in the midst of a prayer meeting. With the tiniest flinches and winces, Finneran conveys Ivanna’s suppressed turmoil, before she stumbles out to the lavatory to find the elder’s voice has been piped in there too, via the PA system. The word of God is omnipresent. Apostasy is a supremely intelligent and gripping drama.