It seems scarcely possible to make a documentary in the open about someone being worked as a slave, rather than having to work undercover to expose it. However, in one of the boldest investigative stories of recent years, Hungarian film-maker Bernadett Tuza-Ritter’s shocking film shows, in almost full view, the exhaustion of being entrapped as a slave and what it takes to get out of it. The bravery in front of and behind the camera deserve high praise. The documentary will surely be used in anti-slavery campaigning in Hungary and beyond in the EU, and it deserves the widest audience.

Marish, the captured woman of the title, has been an unpaid domestic worker for a woman named as Eta in the film for 10 years. Aged 53 but looking at least 25 years older, Marish has been separated from her family and friends, and stripped of her possessions and dignity. Psychologically broken, she is all facial lines, skinny bones, painful body and utter resignation when we first meet her. But in the 18 months during which Tuza-Ritter follows her, her confidence grows and her awareness of the brutality of Eta and her family becomes stronger and more intolerable.

Eta and her brattish family are only heard off screen. It was a condition of their agreeing to the film being made, but the technique only lends them an even more sinister air. They are hard taskmasters with voices from the ether, and we’re left to imagine what these monsters must look like. Petty grievances over the amounts of sugar in coffee carry the threat of physical violence. Every moment has to be accounted for. Marish has been forced to take out loans on behalf of the family. This is a deeply abusive relationship.

Watch the trailer for A Woman Captured

Tuza-Ritter, at least to begin with, was a novice on issues of modern slavery, and it’s probably for that exact reason that her observational filming is so bold. Having met Eta by chance, and effectively paid her for Marish’s screen time, we suspect that even she didn’t initially realise the cruel scale of what she had uncovered. A more experienced film-maker or campaigner, or one working less independently, might have been more cautious about going alone into a slave house, but this one just keeps going, asking Marish unintentionally naive questions to which she responds with shocking frankness. Early on, as Marish goes to her early morning day job (she also earns money for Eta), she casually tells the story of how her daughter was lost to her because of the cruelty of her “owner”. This level of trauma is almost unwatchable.

Some films might have stopped at the point at which the director discovered the misery of Marish’s life, or turned into a legal procedural in which the authorities attempt to free the slave. But, even though we never hear her voice or off-camera opinion, we feel Tuza-Ritter senses a growing trust from Marish, and subtly encourages her to think about another life. Marish begins to tell secrets about her hopes and plans, and the act of saying them out loud starts a chain of rebellion. Early in the film, Marish is clear that there is no one to help her and nowhere to go. Watching her say this, we know it isn’t true – Tuza-Ritter and ourselves as viewers are there and we’re desperate to help. It’s amazing what someone simply paying you attention and listening to you can do.

The arrogance of Eta, in allowing a documentary-maker to film her slave, with no suspicion that it might expose her, backfires on her spectacularly. Marish eventually becomes a hero in joyous fashion, and the depths of harrowing suffering in the first half of the film are surpassed many times over by the euphoric state in which she ends the film. This is far from an an uplifting watch, but it does surprisingly end with some hope. And it is wonderfully constructed, as well as being beautifully shot for a film made in such extreme conditions.

This is the story of one woman’s dangerous bid for freedom, empowered by a documentary-maker without whom she would have remained lost, remarkably captured as it happened at close quarters. Beyond the personal, though, it is a much bigger story about an EU member state where slaves can openly be captured and worked to physical and mental exhaustion, and where there is no effective law for preventing it. The film is an outstanding personal and social-justice achievement.