It's been two years since Sherlock Holmes died, and a few things have changed.
John grew a mustache, and has a girlfriend named Mary, who is a long time friend of Claudia's.
Claudia is a secret agent working for Mycroft, trained expertly in hand-to-hand combat, weapon usage, and multiple languages.After the death of Sherlock and the betrayal of Moriarty, Claudia vowed that she was never going to let herself become a victim ever again. She set aside her differences with Mycroft and allowed him to teach her how to hone her deduction skills. She's still not ok, but at least no she can move on with her life...
But then again, no one considered that Sherlock Holmes was still alive...or that he was coming back to Baker Street.
It has been two years since the world's only consulting detective, Sherlock Holmes, faked his suicide and he is now back to his eventful life at 221B Baker Street.
After he saved 'The Woman' from a cruel beheading many years ago, she returns to London. Upon Irene Adler's return, Sherlock is faced with one of his most difficult challenges yet; the possibility of love.
As an old foe returns, Sherlock, John and Irene, must put the past behind them to survive. This time, however, the stakes might be too high for even Sherlock Holmes.
(Post season 3 of BBC Sherlock)