James lives in an underground house with his parents, Ted and April Mitchum. Forbidden to live underground by his parents, the only link to the outside world of James is an educational show for children called “The Adventures of Brigsby the Bear”. James is obsessed with this show, having a collection of all the tapes and filling the whole room with pictures and extracts from the show. One night when he tries to sneak out, James sees some police cars approaching the house and arrests Ted and April, and he’s taken from there.
James is brought to the police station where he meets Detective Vogel, who worked on his case. Vogel tells James that Ted and April are not his real parents and that he has been in captivity since childhood. He also tells him that Bears Brigsby is not real, but it was an invention of the two to keep him busy. Vogel then presents his real parents, Greg and Louise Pope, and his sister Aubrey daughter.
As they try to readjust James to his new life, he can not take his thoughts from Brigsby, how can he not be real. One night, Aubrey takes James to a party and there he begins to tell his new friends about Brigsby, and then comes up with the idea of making a film based on that character to end the show. Spencer, Aubrey’s friend, who is also a film director, agrees to help James in making this film.