BBC One Releases Sherlock Promo Image before Victorian Christmas Special

BBC One has released a promo image for the upcoming Christmas special of "Sherlock."

The image reveals that the detective duo will indeed be heading back in time to the Victorian era for the upcoming Christmas special. Benedict Cumberbatch as Sherlock Holmes and Martin Freeman as Dr. John Watson are both wearing outfits from that era. Watson's mustache is also a dead giveaway of that time period.

Fans of the hit series, which launched Cumberbatch's career and gave Freeman a BAFTA award, already knew that the special episode would be going back in time. The show's co-creator, Stephen Moffat confirmed in March that the episode would stand alone.

"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 said to Entertainment Weekly.

The plot details for the special have been kept under wraps. Moffat hinted that things will be taking a "darker" turn, but did not reveal anything else about the highly anticipated episode. After the episode, a full series will also air. The details for the fourth season of the show, which is expected to air in 2017, are also unknown.

"Series Four! At last ! It's always special to return to Sherlock but this time it's even more special as we're doing... a special! Not only THAT, we'll then be shooting three more episodes which will take Sherlock and John Watson into deeper and darker water than ever before," Gatiss said in a statement when the episodes were announced. "The whole Sherlock team are terrifically excited to return for four new adventures. The Game is on-again!"

"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 stated.

The Victorian time period would be a nice departure for the Sherlock and Watson, who spent the first three seasons in modern London.

"Sherlock" airs on PBS in the United States. In the United Kingdom, the show can be watched on BBC One. An air date for the Christmas special still has not been released.