The title speaks for itself.

(Y/N) (L/N) works for Mycroft Holmes and has for years, but when Mycroft's brother, Sherlock, fakes his suicide, Mycroft needs someone to take his place. He decides there is no one better than (Y/N) who has nearly identical abilities to his little brother, but is she up for the task of replacing the famous consulting detective? The answer to that question is for Sherlock to answer when he returns and tries to find out just who this woman is that has been replicating his life. {Mature Content}