Director: Jon Stewart
Cast: Gael Garcia Bernal, Kim Bodnia
Certificate: 15

When Jon Stewart took a break from The Daily Show to make Rosewater, the true story of Maziar Bahari, an Iranian journalist jailed in his home country after covering the protests surrounding the 2009 elections, the response was surprise: the comedian was going serious, swapping TV laughs for movie drama. Perhaps, you suspected, he would attempt to pull an Armando Ianucci, combining witty jokes with an edgy subject. But what he does is something even more unexpected.

Gael Garcia Bernal plays the reporter, who goes back to stay with his mum in Tehran. While he and the rest of the cast fall into the trap of people-from-other-countries-speaking-English, though, Stewart immediately establishes a sense of realism by seamlessly inserting handheld footage of events. Maziar (Bernal) interviewing the locals is cut with Bahari's original videos shot from the back of a motorbike, before we see him pretending to be an American spy for a skit on The Daily Show.

This is where Stewart became involved in the story in real life, so it's fitting that it's also where his movie finds its footing: in the intersection between reality and absurdism. The debut director toys with visual flair, as he superimposes exposition onto buildings in the background and floats neon hashtags over the rooftops, but Rosewater's strength lies in the mundane.

After the initial rush of colours and stock types, things are reduced to what is essentially a two-hander between Bernal and his interrogator, Javadi (Kim Bodnia). From the moment that Maziar is blindfolded and locked in a cell, we don't leave the prison's tiny, white walls - a decision that emphasises the claustrophobia of confinement, but also gives the actors maximum opportunity to shine.

Kim Bodnia is terrific - and terrifying - as Maziar's captor, mentally bullying him with repeated questions and a stubborn refusal to listen. Bernal, meanwhile, becomes increasingly desperate, his initial, cool composure breaking out into bursts of sweat and panic. Is he really part of a corrupt regime? Is obeying his new captors the only way to return home? But as he doubts his own sanity, initial accusations of espionage turn into enquiries about Maziar's connection to Anton Chekhov and debates about whether The Sopranos and Empire Magazine count as porn. And suddenly, you find yourself, like Maziar, giggling.

In another filmmaker's hands, this might seem patronising or in poor taste, but Stewart's script (based on Bahari's memoir, Then They Came for Me: A Family's Story of Love, Captivity, and Survival) details almost word-for-word the conversations that actually took place: rather than strive to force comedy into the situation, Stewart lets the clearly smart Javadi talk himself into a hole, teasing out the Kafka-esque silliness of the Iranian intelligence service that he's employed to uphold. Like Four Lions, he's a potential villain made even more disturbing by just how human he is. This mature, restrained approach lets the tone shift back and forth between laughs and horror naturally, finding humour in the darkest of places, while still ramping up the tension of Maziar's 118-day sentence.

The final reveal of his freedom is as rewarding a pay-off as you'd expect, but Stewart leaves his biggest punch for last: a conclusion that turns this personal story of emotional survival into a universal message; a tribute to those reporters who are still being locked up for doing their jobs, and an inspiring reminder that, no matter how many regimes try to suppress the global media, someone is always there with a camera, waiting to tweet about it.