The scriptwriters have said 'there was a "clue everybody's missed" in the second series cliffhanger, which will be revealed to a select audience at an advance screening of The Empty Hearse at the BFI in London on 15 December."
There's a bonus Christmas Special mini-episode for millions upon millions of "Sherlock" fans. They can watch it on BBC's Red Button Service and online on Christmas Day, December 25, 2013.
According to the official synopsis of Christmas Day "Sherlock" mini episode, "Sherlock has been gone for 2 years. But someone isn't quite convinced that he's dead..."