According to the show’s co-creator Steven Moffat, who sat down with EW at South By Southwest, the next episode will take place in Victorian London. And, on the basis of his comments, it may emerge as a spinoff of sorts:
“The special is it’s 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.”
Moffatt’s comments line up with what we learned in July last year. The next feature-length episode IS a standalone Christmas special – that we now know will take place in the late 19th century – which will then be followed by a brand new three-episode season. He went on to tell the trade that the time travelling special has completed shooting and that he’s “pleased with the result.”
That one-off Victorian episode of Sherlock is expected to arrive in the UK sometime in December, quickly followed by a US air date. Cumberbatch, Freeman and Moffatt will be joined by returning co-writer Mark Gatiss and Amanda Abbington as Watson’s wife.