It's the end of the world as we know it, but there are no long shots of mushroom clouds rising over cities or hordes of bedraggled survivors battling over what's left – not even much beyond a few raised voices. Any violence is hinted at rather than depicted – in fact the film's subtlest moment comes when we assume there's been an act of murder, but the scene ends before we see it and we have nothing to prove it actually happened aside from the word of one of the characters, and he has an agenda.

In a way, the possibly violent act that forms the climax of Z For Zachariah is the mission statement of the film. It's not about the end of days or any other such sci-fi concept, it's a slow burning drama about humanity in its rawest state. Faith grapples with science, decency does its best to stave off savagery and even issues of gender and race are raised.

Based on the book by Robert C O'Brien, it centres on a rural farm in the aftermath of an apparent nuclear war that's wiped most of humanity out. For some reason the fallout and radiation has left the valley home of young, pious farm girl Anne (Margot Robbie) untouched, and she's quietly going about her life – harvesting and hunting for food with her dog and believing that her younger brother (who left to look for survivors) is going to come back one day.

Instead, she comes across scientist and engineer John (Chiwetel Ejiofor), dragging a trailer full of provisions and wearing a hazmat suit. When he throws himself joyfully into one of her waterholes Anne risks everything by revealing herself, warning him to come out – the water comes from outside the valley and might be contaminated.

John indeed takes ill, and after Anne nurses him back to health their lives become as idyllic as it seems they'll ever be as they combine their efforts to survive.

But Anne wears her heart on her sleeve and wants to believe there can still be friendship and even love in the world. The staunchly practical (and atheist) John can't help but be won over by her sweet nature, and likewise starts to believe life might be good.

But mine worker Caleb (Chris Pine) soon shows up too, claiming he's been surviving underground and has only come back to the surface after the food has run out. Caleb is as religiously devout as Anne but with the air of sexual threat surrounding him, his arrival throws a cat amongst the pigeons. John sees the way Caleb looks at Anne like he wants her for himself, and he sees the way Caleb looks at him, like he wants John out of the way.

It sets up a triple hander that's very stripped back and pure, much like writer/director Craig Zoebl's first film Compliance. With no effects or hysterics Robbie, Ejiofor and Pine have nothing to rely on but their performances and reactions to each other.

You might think it drags (particularly if you're used to end-of-the world scenarios involving alien invasions or zombie apocalypses), but the best approach is to forget the nuclear wars and danger – all that stuff is just a narrative device to turn a microscope on the hopes and fears of these three people when there's no society around to prescribe their behaviour anymore.