The story has been adapted more than once: the mysterious, somewhat murderous, Phantom of the Opera – the "Angel of Music," a disembodied voice who tutors Christine, a poor chorus girl, until she can take the stage and sing solo. But when she does, and is recognized by an old friend who is now a suitor, the Phantom reveals himself as a hideously deformed man, kidnapping Christine in a fit of jealousy – and the suitor must seek and rescue the girl in the hidden tunnels beneath the opera house. There are stories, books, movies (silent and otherwise), and a musical for the stage.
But what if the Opera-house Ghost really was dead?
It isn't so bad, being a ghost. He watches the people come and go, watches the buildings be built over his hidden grave. (Hidden prison, really; it would be less of a curse if he were only a ghost, with no hope of ever returning to the living.) He gravitates to the place of music, of course. Not only is song the key to his hope, but he likes the music.