James Pope (Kyle Mooney) was kidnapped as a child, kept away from the outside world with nothing but a TV show called "Brigsby Bear Adventures" to keep him connected to the outside world.
When James is rescued and brought back to society, he sets out to make a movie to finish the Brigsby Bear series. He befriends his sister Aubrey's schoolmates and has them help him make the movie.
James gets into trouble along the way, but the movie is complete and shown to a packed house. Brigsby defeats his nemesis Sunsnatcher, and the audience gives James a standing ovation.