Based on a film called "The Devil's Foot", starring Jeremy Brett and Edward Hardwicke as Sherlock Holmes and John Watson. This one particular scene got me really emotional, so why not base a fic of it?

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.)

Sherlock Holmes is a fictional consulting detective in London ~1880-1914 created by Scottish author and physician Sir Arthur Conan Doyle. Holmes, master of disguise, reasoned logically to deduce clients' background from their first appearance. He used fingerprints, chemical analysis, and forensic science. The majority of the stories were first published in The Strand Magazine accumulated to four novels and fifty-six short stories set 1880-1914. All but four stories are narrated by Holmes's friend and biographer, Dr John H. Watson; two are narrated by Holmes himself (The Blanched Soldier and The Lion's Mane) and two others are written in the third person (The Mazarin Stone and His Last Bow). In two stories (The Musgrave Ritual and The Gloria Scott), Holmes tells Watson the main story from his memories, while Watson becomes the narrator of the frame story. The first and fourth novels, A Study in Scarlet and The Valley of Fear, each include long omniscient narration of events unknown to Holmes or Watson