The short version is that it’s the story of Christine, the Phantom, and Christine’s childhood friend Raoul. The Phantom has been Christine’s music tutor, to the point of all but pushing her onto the stage when the lead actress is unable to perform. To keep her in the spotlight, the Phantom makes sure things keep happening to other people in their theatre company, to the point of a chandelier crashing onstage. Eventually the Phantom kidnaps Christine and when Raoul goes down to rescue her, captures him. He gives Christine a choice: stay with him and Raoul lives, or leave and he dies. Christine asks the Phantom what kind of life he’s lived to be able to put someone in a situation like that and that act of giving him a chance persuaded him to tell Raoul and Christine to leave and never tell anyone what happened. The musical leaves it unclear as to the Phantom’s fate after that, whether he remained in his lair or died or something else entirely.