A woman outside a jail in Tehran asks to see her husband. Visiting hours have finished, the guard tells her. The woman pleads: “He’s about to be executed.” Inside, her husband looks up as she walks into his cell, silent, despairing. As the door slams shut, the camera is left staring at the closed door, listening to the woman’s agonised sobs. So begins this restrained Iranian drama about her fight for justice. It’s a film that quietly builds tension, almost suffocating by the end. Made in the austere Iranian tradition, the style is spare, no soundtrack, little to no camera movement – but with a real intimacy between the characters and screen.

Maryam Moghaddam (who also co-directs) plays Mina: one year after her husband Babak’s execution, she is blandly informed by an official that he has been exonerated – the real murderer has been identified and arrested. It’s all been a terrible mistake, everyone is sorry. But there is nothing to be done. “After all, it was God’s will.” As a widow living alone, Mina is powerless. Her late husband’s brother bullies her to move in with the family. Reading between the lines he would like to marry her and his father appears to want to get his hands on the blood money due to Mina as compensation. When she refuses, they threaten her with a custody battle over her daughter Bita (Avin Poor Raoufi), who is deaf.

Then along comes Reza (Alireza Sanifar), a depressed sad-looking man who seems too good to be true. He tells Mina that he is an old friend of her husband – he wants to help out, find her somewhere to live. But is all what it seems? Here the film pivots into a kind of subtle thriller, as Mina and Reza become friends, possibly more. This is a suspenseful engrossing watch, though perhaps with a couple too many plot developments.

• Ballad of a White Cow is available on 10 February on Mubi.