There is a painfully despairing and defeated feel to this film by the Serbian documentary-maker Mila Turajlić, looking back at a century of politics and revolution in her country through the Belgrade apartment in which she grew up. (Apartment really is the right word; flat wouldn’t do the high ceilings justice). The block was built by her great-grandfather, a government minister who signed the document that created Yugoslavia in 1918. After the communist revolution, the authorities confiscated half of the family’s living space, deeming it too grand and bourgeois. The sitting-room door has been locked ever since. On the other side lives the woman who was installed there in 1947; she’s 90.

The true subject is the director’s mother, Srbijanka, a retired engineering professor and political activist – she was a leading figure in the opposition movement against Slobodan Milošević’s regime, rallying crowds of thousands, many of them students. What shines through in the film is Turajlić’s awe of her mum and a question: what made Srbijanka (what makes anyone) stand up and fight? “You knew exactly what to say and people listened,” Mila says with wonder. Her mother, plain-speaking, grey hair bluntly cut short like a nun’s, cigarette in hand, simply shrugs. She believed her generation had failed her students, and she felt responsible for what they were living through.

The intimidatingly dense discussion of Serbian politics here is possibly off-putting if you don’t come with an interest. Depressingly, towards the end of the film – shot over five years – Srbijanka is named by a rightwing group on a list of Serbia’s “30 biggest traitors”. It is 2015, and Milošević’s former information minister is prime minister. Srbijanka is a Cassandra of liberal internationalism; she’s pessimistic about the future, and her warning to be vigilant to the rise of nationalism and strongman politics perhaps has resonance beyond Serbia.