Sherlock Season 4 Release Date: "Sherlock" will be back with for season 4 in 2016, but first the BBC will airing a special Christmas episode in 2015. The British crime drama based on Sir Arthur Conan Doyle's Sherlock Holmes detective stories is moving to Plan B to Top "Sherlock: Series 3."

"Of course, it's far too early to say what's coming, but we're reasonably confident that the very next thing to happen to Sherlock and John, is the very last thing you'd expect ..." BBC Sherlock's creator, Steven Moffat told Entertainment Weekly.

"We have a plan to top [Season 3]," Moffat continued. "And I do think our plan is devastating. We've practically reduced our cast to tears telling them the plan ... we're probably more excited that we've ever been about Sherlock.  It will be challenging place to go. We always start with a re-introduction that builds toward a darker climax - we might just be going darker [from the outset]. We got a very, very good set of ideas."

Benedict Cumberbatch and Martin Freeman star as Sherlock Holmes and John Watson. Andrew Scott plays Sherlock's nemesis Jim Moriarty, whose fate was left undetermined in the last season.

The special 90 minute holiday episode of  Sherlock won't be connected to Season 4. Holmes and Watsonwill go back 100 years to roughly the same time period as Sir Arthur Conan Doyle's stories.

"The special is its own thing. We wouldn't have done the story we're doing, and the way we're doing it, if we didn't have this special. It's not part of the run of three episodes. So we had this to do it - as we could hardly conceal - it's Victorian. [Co-creator Mark Gatiss] and me, we wanted to do this, but it had to be a special, it had to be separate entity on its own. It's kind of in its own little bubble," Moffat told the crowd at a South by Soutwest conference.

Sherlock also stars Amanda Abbington (Mary), Louis Brealey (Molly Hooper) and Jonathan Aris (Anderson). Suzie Lavelle joins Sherlock season 4 as Director of Photography. Tom Hiddleston from "The Avengers" is rumored to be joining the cast as Sherlock's third brother.

BBC's "Sherlock has been a critic's favorite and an audience hit. Cumberbatch has become a major star since it began in 2010.