What is the theme in The Berlin Stories: The Last of Mr. Norris, Goodbye to Berlin by Christopher Isherwood?

The mystery of the individual is a theme in this book. There are several instances, throughout both "The Last of Mr. Norris" and "Goodbye to Berlin," in which an individual's true identity (feelings, motivations, perspectives, beliefs, etc.) are kept hidden from the individuals around him/her. A primary example is the title character of "... Mr. Norris," who keeps the narrator (William) guessing about who he truly is and what he's really about for the entire narrative.