Catfish follows the story of Nev, a young photographer who lives with his brother Ariel and friend Henry Joost in New York City. When eight-year-old artist Abby Pierce sends Nev a painting of one of his photographs, they strike up a friendship via Facebook. It doesn’t take long before Nev notices Abbey’s attractive older sister Megan, a veterinary technician, dancer and songwriter who lives in Gladstone, Michigan.
Nev’s brother Ariel and room-mate Henry, decide they want to make a documentary that follows Nev’s blossoming online relationship with Megan, but it doesn’t take long before the two discuss meeting up. When Nev realises that the music Megan has been apparently recording has in-fact been ripped from YouTube, it doesn’t take him long to work out that Megan and Abby have made other false claims.
Ariel pleads with Nev to continue the relationship for the sake of their new film. Reluctantly, Nev agree’s, and it isn’t long before the three head to Michigan to confront Megan.
When they arrive, they head over to a Angela’s house. As the pair drive to Abby’s house, Angela announces she has cancer and is beginning chemotherapy shortly. But when they arrive to see Abby, she says “you’re confusing me”, as Nev repeatedly asks her about her art.
When Nev wakes up the next morning, he has received a message from Megan saying she is unable to meet him because she is checking into rehab. Upset, Nev sits down for a serious chat with Angela, but she breaks-down and admits she made the whole story up. She tells Nev that Megan is a friend of a friend, when in fact the pictures of Megan are really of an unrelated woman in Washington. Unable to stop lying, Angela claims that her real daughter Megan really is in rehab, but it turns out that Megan has been estranged from the family for a long time.