The first full-length trailer to the one-off Victorian-Era episode that kicks of "Sherlock" season 4 has officially arrived. The trailer reveals Sherlock Holmes (Benedict Cumberbatch) and his partner Dr. John Watson (Martin Freeman) as they once again team up to solve another mystery, this time set in the 19th century.

However, the trailer does not reveal who the main villain is or what the case will be about. Sherlock mentions "ghosts of his past" and the trailer repeatedly shows people in pointy hats, indicating they may be members of the Ku Klux Klan aka the KKK.

The group was slightly referenced in the season 1 episode "The Great Game." This was a reference to the Arthur Conan Doyle story "The Five Orange Pips." According to a report from Screen Rant, it is possible that series creator Steven Moffat is going back full circle to tell the story in full and in the chosen time period.

Moriarty (Andrew Scott) is nowhere to be seen in the trailer and his character does not play of any signficant importance in "The Five Orange Pips," although it is possible he may appear in a cameo or may simply be referenced before the episode ends.

The trailer does showcase the Victorian version of Sherlock and Watson's apartment on 221B Baker Street as well as the Victorian version of Officer Lestrade (Rupert Graves). Despite the spooky tone of the trailer, there are a few tongue-in-cheek moments such as Watson mentioning the time period and Watson forcing Sherlock to wear his hat.

While previous special episodes were treated as Christmas Specials, there is no indication of such a theme in the trailer for the Victorian Special and there are speculations that the special episode might be pushed to a January 2016 release date. The trailer does not give a release window although it is likely the BBC will announce its air date soon.

"Sherlock" season 4 proper, which will continue the contemporary setting of the series, is expected to begin production in mid-2016 and air by 2017.