Film: Catfish

This is denied by film-makers Ariel Schulman and Henry Joost, who chose as their subject matter Ariel’s brother Yaniv, or Nev (pronounced Neev). All three are partners in an excruciatingly hip New York production company called Supermarché, where photographer Nev specialises in taking photos of dancers while the other two make commercials and documentaries.

It’s quite easy to take an instant dislike to this trio of cooler-than-thou, shamelessly narcissistic Manhattanites, who seem to have nothing better to do than to loll about gossiping on their iPhones or videoing each other. Ariel seems infatuated with his brother’s photogenic prettiness and, in response to suspicious inquiries about why he happened to be filming Nev when the film’s gobsmacking plot fortuitously sparked into motion, says he just likes filming him all the time because he's so interesting. Nev is all perfect teeth, Chanel-ad stubble and boy-band floppy hair, a walking glossy catalogue of male grooming tips, and though he protests that he doesn’t want to be the focal point of a movie, you can’t imagine that he ever wanted to be anything else.

But it’s part of Catfish’s seductive pull that just when you’re about to write off both film and film-makers, the piece veers abruptly off-road and undergoes a dynamic personality transplant. What looked like an egregious exercise in vanity film-making turns mysterious, scary, then almost tragic. Suddenly its hooks are in you pretty deep (the photogenic Nev on his iPhone, pictured right).

By accident or design, Catfish has also managed to make itself critic-proof, at least in as much as the structure of the film makes it very difficult to write about without giving away the whole point of the exercise. The story begins to roll when Nev receives a painting through the mail from an eight-year-old girl called Abby, who lives in Ishpeming in rural Michigan. The painting is based on one of Nev's dance photographs. Nev is flattered and intrigued enough to begin an online friendship with Abby and her web-chaperone mother Angela (whom a later painting by Abby will depict as a vision of serene loveliness). Abby, Angela tells them, is a juvenile art prodigy whose paintings are fetching thousands of dollars and are being exhibited in any number of local galleries. Meanwhile bundles of them keep turning up in the mail at the Supermarché office (pictured below).

The developing relationship prompts Ariel and Henry to start recording it on camera, and soon Nev is sliding in deeper than he intended. He finds himself befriended on Facebook by increasing numbers of Abby's friends and relatives, not least her rather gorgeous sister Megan. Before long, Nev and Megan are enjoying a titillating "sexting" relationship (Nev eventually gets to read out their correspondence off his iPhone, to his real or possibly re-enacted embarrassment). Shots of Facebook walls, iPhone screens and Google Maps images are used to tell the story while also banging home the technology and new-media message.

When Nev's attempts to fix up a real-life meeting with Megan are met with a string of evasions, the film-making trio start to grow uneasy. They decide they'll pay an unannounced visit to Abby, Megan and co, since they have to head up in that direction for another assignment anyway. They pile into a car bristling with iPods, iPads, iPhones and Macbooks, and though for a moment it looks as if they may be straying into some kind of Michigan Chainsaw Massacre frightmare, what they discover turns out to be far more unpredictable and troubling.

Can't tell you much more, except to say that what looks like a comedy about social networking turns out to be an examination of the gulf between cyberspace and the "real" world. Even if Nev and co have made the whole thing up, what the film says about emotional need and hard compromises feels true enough. It's like that George Harrison lyric - "we were talking about the space between us all".

• Catfish is on release from Friday, 17 December