Benedict Cumberbatch and Martin Freeman will be returning to the series as the famed duo Sherlock and Watson. According to reports, Sherlock and Watson will be travelling back to the Victorian Era in Sherlock Season 4.

According to show runner Steven Moffat, it is confirmed that the time travel concept to the Victorian Era will take place during the 90-minute special, which will serve as a "stand-alone" episode. The time travel concept will not be part of Sherlock Season 4.

"The special is its own thing," Moffat said  "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."

Sherlock Season 4 will also have some major shockers, which will leave fans of the BBC detective series on the edge of their seats.

"A special, plus a new series of three episodes -- it's a record-breaking run! 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 ..."  Moffat teased.

While the show has always been  serious in nature, there have been comedic undertones that have given the show its loyal fanbase. However, Moffat has said that the series will grow 'darker' in the upcoming episodes. Will this mean the death of a beloved character?

"We're going to try to take it somewhere we've never been before - and I don't mean outer space," said Moffat. "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."  

Sherlock Season 4 will air sometime in 2016.

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