Catfish (12A)

Caught hook, line and sinker

There's a peculiar smell coming off Catfish, a documentary narrative that examines the digital possibilities of fakery yet might just be a fake itself.

The story it purports to tell is involving, even haunting, and it gets to the heart of a very modern phenomenon: how the internet has brought people closer and at the same time given them licence to falsify and mislead. It is a kind of low-budget pendant to the Facebook drama The Social Network, one that offers a more unsettling portrayal of the personal chaos engendered by online "friendship". The truth is out there, the phrase once ran – but how would we recognise it in this virtual world?

It starts in 2008, when a 24-year-old New York photographer, Nev Schulman, is contacted online by an eight-year-old Michigan girl named Abby. She has sent him a painting she has done, copied from a photograph of dancers Nev had published in a local newspaper. The quality of the painting suggests that Abby is a child prodigy; via Facebook Nev corresponds with her, with her mother Angela, and with Abby's half-sister Megan, a pretty blonde and part-time model, sending each other presents and photographs. By now Nev's brother Ariel and their friend-cum-business partner Henry Joost have started filming this strange one-side-only relationship, and in particular the burgeoning cyber-romance between Nev, himself quite a looker, and Megan. They even get to talking on the phone: "Very mature voice", reckons Nev of his distant teenage sweetheart. He's so besotted with her he even Photoshops their images into a soppy two-shot.

What at first seems quite innocent ("When did you start calling each other 'babe'?") becomes slightly iffy. Megan starts sending Nev songs she claims to have written for him. A quick search on the web reveals that the songs have been downloaded from YouTube, and gradually suspicion leaks into the air like marsh gas. Nev wonders aloud if the girl he's been smooching online for months is – the horror! – a guy. Was it perhaps at this point that Ariel and Henry, amused onlookers up to now, decided there might be a feature film here? They surely couldn't have known beforehand what surprises it would turn up. As their camera watches Nev talk on the phone to his Michigan friends, we get the impression of events rapidly unfolding before our eyes, and his mixture of confusion and anxiety becomes ours as well.

It is established that Angela and Megan are not all they seem, so, using Google Earth maps to pinpoint locations, the two film-makers and Nev go on the road to deepest Michigan in search of answers. What they discover is – well, it would be wrong to let this cat out of the bag, because the twist ought to be savoured for the shock it is. Yet for the audience the tension is shadowed by a persistent concern that the film isn't telling it straight. As their car heads through dark rural lanes, with only a SatNav to guide them, the rustle of a Blair Witch-style mystery descends on proceedings. Who in their right minds would pitch up at a lonely farmhouse at 2.30am and knock at a stranger's door? It's not just risky – it's also bad manners. The whiff of exploitation becomes unignorable as Nev, wired for sound beneath his shirt, finally gets to meet Angela, though what's revealed actually splits our sympathies right down the middle. Nev has been naive, especially so for a cool, young urbanite, but his forbearance in reaction is gracious. Angela's behaviour initially seems unhinged – "it's not malicious, it's just sad" – but further investigation hints at an inner life of tragic complexity. This is the way real people are, the film tells us.

And yet... and yet, the way the film tells it keeps provoking our suspicion. The scenes sometimes run together too smoothly, and you wonder if they haven't reshot parts of it as they went along. Or did they follow the trail of Nev's beguilement for real, then reconstructed the whole thing as docudrama? With this genre it's become increasingly difficult to tell the real from the fake. Even the fly on the wall seems to be in on the act. Though it seems gullible of me in retrospect, I took most of I'm Still Here, the recent Casey Affleck "documentary", as a faithful account of Joaquin Phoenix's public disintegration. For one thing, why would anyone choose to perpetrate such a prank? Catfish, whatever its degree of manipulation, at least aims for higher truths, about identity, about loneliness, about communication. The name of Andrew Jarecki as one of the producers vouches for its seriousness, this being the director of Capturing the Friedmans, a 2003 documentary begun in jest – the portrait of a children's clown – before it stumbled on a dark family history of abuse. It's the kind of lucky break a film-maker craves, though one must suppose the Friedmans didn't feel quite the same way about it.

You could argue about Catfish for hours and still not reach a consensus. That's part of its cleverness, too. For some it will be a cautionary tale about a new alarming preference for virtual contact over the human sort. To more cynical observers it will be an exercise in opportunism from people who ought to know better. All I can say for certain is that it will absorb you from the first frame to the last.