American fans of British television are used to being jerked around a little bit. Entire series will run for a combined ten episodes, broken into two comically short seasons, with about two years in between. It makes Mad Men seem like it’s on a rush order.
Well, you can set your cynicism aside for Sherlock, which will be returning for a fourth season (of probably only three long episodes) and a special before that airs, or even shoots.
The special will adhere to the storyline and resolve some season 3 questions, so think of it more as an early first episode of season 4 than something standalone. You know, like you would normally think of a special.
The special begins filming early next year, and the season starts filming late next year. In the meantime, get reacquainted with the first 9 episodes. That should take you a day or so.