What is the theme in The Phantom of the Opera by Gaston Leroux?

Appearance and reality is a theme in this story. The fact that The Phantom of the Opera takes place behind the scenes of the opera almost automatically draws readers' attention to the disparity between reality and appearances. Leroux gives backstage details, starting with the dancers who line up in the first chapter, gossiping, and continuing on to point out the backdrops and the business arrangements that few opera goers are allowed to see.