"Don't let anyone tell you what it is," cautions the tag line for Catfish — "it" apparently being the Big Twist powering this "reality thriller" torn from today's spam filters. In respect of the time-honored code that says you never tip another carny's hustle, I won't say what "it" is either: You'll have to find that out on your own, sucker, as directors Henry Joost and Ariel Schulman find a rare specimen in Schulman's brother Nev — the last 20-something dude in the universe to suspect that maybe not everyone on the Internet is exactly who they say they are.
It looks like a documentary; it just happens to have the same premise as the Robin Williams/Armistead Maupin yarn The Night Listener, with all the necessary plot-advancing developments neatly caught on (or arranged for) camera. Even so, for the first half, as Nev gets in deeper with his hot new online acquaintance, it builds genuine curiosity and suspense about how the filmmakers are going to reconcile the cinéma-vérité feel with the pulpy inevitable on the story's horizon. Turns out they can't: The "twist" is such a foregone conclusion that its pathetic humanity registers as a failed switcheroo, not deeper insight into the phenomenon of digital fantasy lives.
I'd feel more charitably toward Catfish, which is assembled with skill, if the movie's venal ad campaign didn't reflect something tawdry in the movie itself — namely, the way it rigs a sad, mundane slice of life for a contrived gotcha, hardly redeemed by the idea that we might be looking at real desperation and seeing only anticlimactic plot machinery. The ad campaign hard-sells Catfish as a Paranormal Activity-style spookfest, a tactic the filmmakers have endorsed in interviews. But the shameless bait-and-switch the trailer pulls on viewers is exactly the same thing the movie's "catfish" does to Nev. If Catfish has any lesson, it's that bottom feeders love company.