The upcoming episode of "Sherlock", which will be a Christmas special, will see Benedict Cumberbatch and Martin Freeman, who play Sherlock and Dr Watson respectively, in Victorian era.

The air date for the one off episode has yet to be announced, but it is believed the episode will be aired sometime around Christmas. The one-off episode is said to be based on Sir Arthur Conan Doyle's 1892 story "The Adventure of the Blue Carbuncle."

Besides their clothing, the mannerisms of the two lead characters will also undergo a transformation with Sherlock becoming less bratty, and Watson becoming more upright.

"[Sherlock] the manners of the Victorian gentleman, which he doesn't have in the modern version," showrunner Steven Moffat said during the Television Critics Association press tour, reported IGN.

"So he is a lot less brattish when he's back. And Dr. Watson is a bit more upright. They're the same people, seen through the prism of a different time and fitting in to a different society. I would say this Sherlock is a little more polished, and he operates like a Victorian gentleman instead of a posh, rude man, which he does in the modern too," the showrunner said.

Moffat was also questioned about why he and Mark Gatiss decided to do the one off episode and the inspiration for setting it in Victorian era. However, he noted that the episode won't explain why Sherlock and Watson are in the era.

"Mark [Gatiss] and I were having a fun day on set because he was doing some second unit shooting with some evil monks. It was the prequel, and because I think we found an old prop that was on the original Titus, so we were having a geek day. Gosh, what a surprise. And then we just thought 'could we ever just do maybe one scene or some dream sequel or something?' And then we just thought, you know, 'why don't we just do it? Why don't we just do a Victorian one?'"

The Christmas special will be followed by the fourth season of the detective drama. However, shooting for the three episode season will not begin until spring 2016.