The story of a pious introvert whose religious conviction begins to crumble under the weight of a cruel and strange existence, Buddy Boy is a study of faith, obsession, alienation and madness. The film's title character, Francis, lives with his invalid, abusive mother in a dingy tenement apartment, and has suffered a life of unrelenting misfortune and brutality. Over time, he has withdrawn from the world and into himself, silently observing others rather than interacting with them. His only solace has been his Catholicism, but he has begun to question his faith in a loving God who could countenance so much evil and pain. When he discovers he can see into the apartment of a beautiful, mysterious woman from his own back stairs, Francis cannot stop watching her, even after he meets her and they become romantically involved. Unable or unwilling to believe that she could actually love him, he becomes ever more obsessive in his voyeurism.