It's often forgotten now, but when Sherlock debuted in 2010, the modern setting was perceived as crucial to its appeal. Few characters have been resuscitated with such tiresome frequency as Conan Doyle's iconic crime fighter and the choice of contemporary London as a backdrop was regarded as a vital innovation on the part of show-runner Moffatt. Of course, we soon discovered that the real magic was the dynamic between Cumberbatch and Freeman and this element was preserved wonderfully as the New Year special whooshed back to 1895. Amid the picturesque gloom of gothic London, their banter retained its sparkle while the absence of the internet and smartphones permitted Holmes's genius to shine even more brightly. He seemed twice as smart now that none of the other characters could second-guess him by sneakily consulting Wikipedia.