The Case of the Phantom (Sherlock x Reader)

Paris, France 1889. Sherlock Holmes and John Watson were sent to Paris to investigate the strange Case of the mysterious 'Phantom' that should haunt the Opera House ‚Maison de Muse'.
Both men encounter unbelieve things. But when Sherlock met (Y/N) (Y/L/N) a dance in the Opera everything turned into something neither one of them had seen coming.

(I'm not good at summeries. Or English for that matter. Please excuse me for my bad English.)