But in that regard, the BBC released on Christmas Day a 7-minute “mini-episode” that the BBC released on for streaming online. It's written by the two series co-creators, Mark Gatiss and Steven Moffatt. Though it's being promoted as a "mini-episode, it’s really just a 7-minute PR teaser to prepare audiences for the third season, but it’s still a clever idea to do.
At the end of Season Two, the series did its homage to "The Final Problem" story by Sir Arthur Conan Doyle, where Holmes and Moriarty supposedly fought to their joint deaths going over the Reichenbach Falls. The episode was called..."The Reichenbach Fall." So, Holmes, in the TV series, was left presumed dead. Which brings us to the mini-episode, titled, "Many Happy Returns."
(Side note: Though it hasn't gotten much attention -- probably understandably -- Freeman and Cumberbatch reteamed before this. For the sequel to "The Hobbit"! Freeman, of course, stars as Bilbo Baggins, and Cumberbatch is the voice of the dragon, Smaug.)