Enrique Claudin (Claude Rains) is a mild-mannered violinist in the Paris Opera House orchestra. He uses his income to pay for beautiful singer Christine DuBois' (Susanna Foster) lessons - without her knowledge, as he worships her from afar. However, tragedy strikes when Enrique believes that a publisher has stolen a concerto he has written, which represents his life's work. Enraged, Enrique strangles the publisher, but has acid thrown in his face in the process. Horribly burnt, he hides in the sewers beneath the Opera House, and, now half insane, devotes himself to furthering Christine's singing career.