In Paris, a violinist at the Paris Opera House loses his job after a confrontation with the new owners over a deterioration in his performance, a result of his progressively worsening hearing. This misfortune occurs after he discovers his compositions being published under the publisher's name, leading to a violent altercation that disfigures his face and forces him to flee into the catacombs beneath the opera house. There, he crafts a masked identity for himself, becoming an unseen presence inhabiting the shadowy depths. His profound love for music and an unyielding passion for a beautiful, young soprano drive him to watch over her career from the shadows, aiding her ascent to stardom through manipulating events around her.

As the mysterious benefactor's influence grows, so does the intrigue and terror among the opera house's cast and crew. Amidst rehearsals for a new production in which the young soprano is to take a leading role, accidents and strange occurrences begin to stir fear. The masked figure emerges from the shadows, employing both intimidation and subterfuge to protect the object of his obsession and ensure her success. His actions set off a series of events that ripple through the lives of all associated with the opera, culminating in a crescendo of drama that threatens to unveil the dark secrets lurking within the opera house's walls.