It hardly needs to be said that there is grim news in Patrick Farrelly and Kate O'Callaghan's excellent documentary about female genital mutilation. The practice itself is sufficiently horrific to make much of Jaha's Promise hard to hear, but the picture is also fearless in revealing the wider misogyny from which it springs. Forced marriage, spousal abuse and FGM are all tied together in a knot of intractable abuse.

This is, however, ultimately a positive film. Its makers, who previously directed the impressive Nuala: A Life and Death, about Nuala O'Faolain, focus on a hugely charismatic, impressively determined young Gambian woman called Jaha Dukureh. We begin with apparently idyllic shots of her daughter playing outside their house in Atlanta. Dukureh then talks us through her own horrible experiences. Initially, she didn't even understand what she had been put through as a child. It was only after Dukureh was pressed into marriage with an older man in the United States that she realised how her body had been mutilated. She made a promise to her daughter that, if she could help it, future generations would not have to suffer such physical and mental torment. Dukureh separated herself from her husband and became involved with a campaign group called Equality Now. She travelled to her home country and engaged with prejudice and resistance. But nothing is stopping her.

FGM is one of those subjects that make some western liberals uneasy. There is too often a reluctance to go against unfamiliar cultures and traditions. Told in brisk, digestible fashion – in the company of a charming campaigner – Jaha's Promise cuts straight through such confusion to hammer home the core inhumanities. It clarifies and simplifies. Most importantly, it confirms that campaigning can make a real difference. Worth heeding.