It was Martin Freeman who first dropped the hint that the producers of "Sherlock" are planning a one-off special episode. BBC and Stephen Moffat, co-writer of the show, later confirmed Freeman's hint.
"A special, plus a new series of three episodes -- it's a record-breaking run!" Moffat said in a statement. BBC One said on Twitter, "Miss me?" #Sherlock, the hit @BBCOne drama, will return for a Special, followed by a series of three new episodes."
The production of the one-off special episode, which is reportedly a Christmas special episode, is set to begin early 2015. BBC One shared on Twitter, "Shooting on the #Sherlock special will begin in January 2015, with the series shooting later next year."
There are speculations that the Christmas special episode is likely to be based on Sir Arthur Conan Doyle's short-story, "The Adventure Of The Blue Carbuncle." Den of Geek reported, "With its playful plot, lack of murder or violence, and frothy story of a hapless jewel theft, "The Adventure Of The Blue Carbuncle" essentially is a nineteenth century Christmas special." The writers and BBC have not yet revealed the story of the one-off special episode.
Meanwhile, there are also speculations that Tom Hiddleston might join the cast of "Sherlock" as the third Holmes brother. Mycroft had alluded to the third brother in "Sherlock" Season 3 finale. Hiddleston is reportedly the fans' favourite when it comes to choosing the actor who can portray the role of Sherlock and Mycroft's brother. "Tom would be wonderful in "Sherlock." But he only does movies now. What can I say? I'll ask him if you like," Mark Gatiss, who plays Mycroft and is the co-writer, teased during an interview in Brazil, as quoted by Mirror.
The production of the three episodes of "Sherlock" Season 4 is expected to begin later in 2015. There are reports that the new season production had to be pushed ahead because of Benedict Cumberbatch and Freeman's busy acting schedules. According to reports, the production on Season 4 was originally scheduled to begin in autumn 2014.
"It's taken a little while to get the dates sorted as none of the boys are exactly sitting back twiddling their thumbs but there was unanimous goodwill to make this work, so we're thrilled that 221b is going to be inhabited again," Sue Vertue, executive producer at Hartswood Films, said, as quoted by Indiewire.