When Nev first saw Megan, he thought she was beautiful. The first time he heard her play piano, he told her she sounded like a professional. After they stayed up full nights talking, Nev would later confess to his brother that he thought he was “falling for her.” The only thing that was keeping the two apart was the fact that they had never actually met.

The documentary “Catfish” follows a romance that is untraditional in many senses of the word ó most evidently in the fact that neither of the two lovers had seen each other outside of Facebook.

It started when Nev, a freelance photographer in New York City, received a painting of one of his photos in the mail.

It was from a little girl named Abby from Michigan, who said she saw his photos on the Internet and wondered if he could send her more to paint.

Soon, a full-on Internet correspondence blossomed, first with Abby, then her mother Angela, and finally her half-sister Megan. Nev’s brother Ariel Schulman and his friend Henry Joost filmed the whole thing, hoping to eventually make a documentary about how the Internet affects human relationships.

But what started out as a simple documentary about love in the cyber-age turned into something much more disturbing when Nev begins to wonder if the Megan on the Internet was the same Megan he would find in real life.

Clues begin to emerge in the forms of strangely similar sounding YouTube recordings of the songs Megan sent Nev, and investigations into the art career of little Abby. When Nev, Ariel and Henry finally decide to try to meet Megan and her family in real life, they have their own sneaking suspicions about who might meet them at the end of their cross-country journey.

They’re wrong. And when Nev stares slack-jawed into the camera at one point near the end of the film, speechless, you’ll be right there with him.

I won’t say any more, except that the crashing conclusion to this film stayed with me for days. What makes “Catfish” brilliant, besides the sheer luck that Ariel and Henry were there to record the whole thing, is its subtlety.

There is no doubting that this is real life. The courtship that Megan and Nev share, though technology-assisted, is awkward and endearing in a way that can’t be scripted.

The audience witnesses two people fall in love, and given what comes after, it resonates almost hauntingly over the rest of the film. There is no doubt that something real was shared between Nev and Megan.

But after the revelation of the finale comes, the audience is left to wonder at what cost we pay for human connection.

The filmmakers are also careful not to be exploitive of the stories they found when they turned off the computer and stepped into real life.

There are no real villains in this story, just lonely people. Before watching the film, some people might doubt the “Gotcha!” moment was authentic; that Joost and Shulman didn’t do a little investigating of their own before driving to Michigan to unearth the truth.

Any suspicions, however, are flipped and destroyed when you see who opens that door.

How well do you think you know your “friends”?