The upcoming "Sherlock" special, which is no longer called a Christmas Special, will be a stand-alone episode set in the Victorian era instead of in the modern day. According to the Hollywood Reporter, showrunner and executive producer Steven Moffat also explained that this means the titular character will be portrayed quite differently.
Benedict Cumberbatch and Martin Freeman will still play Sherlock and Watson, respectively, but because they will be in the Victorian era, which the original stories by Arthur Conan Doyle were set in, this means they will be portrayed differently compared to how they are played in the regular seasons.
"Sherlock the manners of the Victorian gentleman, which he doesn't have in the modern version," he said. "So he is a lot less brattish when he's back then. And Dr. Watson is a bit more upright. 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 report also confirms that the portrayal of the main characters aren't the only aspects changing due to the different time period. According to Moffat, this will be the perfect opportunity for them to focus on a ghost story. In the regular series, the only ghost-like case Sherlock and Watson solved was the "Hounds of Baskerville" case.
"Ghost stories work better in a Victorian setting," he said. "Other than that it's remarkably similar."
According to a report from /Film, this will be the only time that they veer away from the modern setting of the regular series. They also see no reason to explain why the special is set in the Victorian era as they never had to explain why the characters in the regular seasons are in the present day.
Following the special episode, Moffat and the rest of the BBC crew will commence production of "Sherlock" season 4 by 2016 with a premiere date estimated to be in late 2016 or early 2017.
