The World to Come is a tragedy and a love story – and also a puzzle, courtesy of the title. Does it mean the afterlife, the entry into paradise that will be recompense for all the hardship and injustice we’ve suffered here? Or does it mean the future: that progressive yearned-for place in which current bigotries will be abolished, and in fact the place from which we, in the 21st century, are looking back on this tale from the 19th, confident that we are freed from these bygone characters’ constraints, content that we understand what is going on and they may not?

The director is Mona Fastvold – who also wrote and directed The Sleepwalker and wrote the script for The Childhood of a Leader – working from a screenplay by Ron Hansen and Jim Shepard, adapted from Shepard’s own story. In a wintry US frontier settlement in 1856, a farming couple have it brutally hard: they are Abby (Katherine Waterston) and Dyer (Casey Affleck). Both are equally disappointed with life and vaguely ashamed of themselves for being so: Dyer yearned to be an engineer, his real passion, and Abby is oppressed with the dull weariness of a woman’s lot. Their infant daughter died of diphtheria the year before, leaving them both numb with grief.

But quite accidentally, Abby’s chores have allowed her to cultivate an inner life. She has to keep a diary, the purpose of which is to keep track of various housekeeping jobs, and uses this to confide her hopes and fears. It is this diary, with its handwritten date entries and Abby’s voiceover, that provides the narrative structure and the final revelation of “hidden” diary entries in montage, the accretion of moments in a hidden existence: it is a storytelling coup.

Abby’s world is turned upside down when a new couple moves nearby: the dour and ironic Finney (Christopher Abbott) whose frustration and self-hate and dangerously suppressed anger is at a far higher level than Dyer’s, and his wife, Tallie (Vanessa Kirby), charismatic, beautiful and not-so-secretly contemptuous of a man’s world in which she is not appreciated.

Kirby and Waterston show with great actorly skill and zeal two people falling head-over-heels in love at first sight, utterly and passionately. All at once, they are inseparable. Abby is bewitched by Tallie’s flirtatious charm, Tallie by Abby’s shy sobriety and idealism. And at first, the menfolk are reasonably content for this friendship to go ahead, grateful for something to pacify their wives. But then they sense there is something more to it, and Affleck and Abbott, though playing very different people, show how these men do not have the emotional language to express what they are feeling; Finney and Dyer are angry at each other and themselves for failing to control this situation. A horribly constrained and tense supper party is a symptom of this.

Period-transgressive love stories are, perhaps, nothing new: Céline Sciamma’s Portrait of a Lady on Fire emerged in 2019 and Francis Lee recently gave us his Victorian tale Ammonite. Fastvold’s film is distinctive in that she shows us how physical constraint and violence are part of the fabric of living. At one stage, Dyer ties Abby to a chair and administers laudanum to control her rage-filled grief at Tallie’s absence – and more violence is to come. Fastvold shows that this is a way of life in which the vast majority of emotion and feeling, and consciousness itself, is suppressed, like a virus in lockdown.

It is suppressed partly by religion but partly by sheer exhaustion. These people are pioneers, and they have sacrificed themselves to build a prosperous way of life that might one day, in the world to come, be appreciated by their descendants, with the luxuries of leisure and culture; Abby is in awe of how her grandmother had it even harder than her. She pays 90 cents for a heartbreakingly modest item for herself: an atlas, in the pages of which she can roam the world, free. Right now, her emotions are buried. But the very secrecy, the very lack of acknowledgment, makes Tallie and Abby’s passion for each other all the more extravagant and real.

• The World to Come is released on 23 July in cinemas.