Whatever remains, however improbable, must be the truth! (Sherlock fanfic)

We all know the great and only consulting detective in the world Sherlock Holmes, right? Well, somewhere in London, there is another great mind running around the city. A HIDDEN one. This is the story of how Mr. Holmes (and his "collegue" John Watson) encounter this small but brilliant girl. (Between "Scandal in Bulgravia" and "Hounds of Baskerville"