Henry Darger spends most of his life as a solitary janitor in Chicago, attending Mass daily and speaking to almost no one. After he dies in 1973, his landlord Nathan Lerner discovers what he left behind in his rented room: a 15,145-page manuscript called The Story of the Vivian Girls, along with hundreds of drawings and watercolors, some over ten feet long, illustrating a war between child slaves and the adults who enslave them. The film reconstructs Darger's life from the sparse evidence available, his childhood in an asylum, his years of menial work, his self-taught technique of tracing figures from magazines and comic strips, since interviews with the man himself do not exist. Neighbors and acquaintances who barely knew him describe a person who gave no hint of the world he was building in private. The film treats the room itself, cluttered floor to ceiling with his materials, as the closest thing to a portrait, and lets the epic strangeness of the artwork stand in for the biography no one got to record while he was alive.