"Sherlock" Season 4 is currently in development and, as previously confirmed, will only have three episodes. Masterpiece and PBS recently featured the first official photo of Sherlock Holmes (Benedict Cumberbatch) and John Watson (Martin Freeman).
In the "Sherlock" Season 4 photo, the two detectives were standing side by side against a dark gray wall. Watson had a dark plaid shirt buttoned up to his neck and slicked back hair. Sherlock had a dark suit on, albeit without a tie, and was looking straight at the camera. His arms were crossed over his chest, just like Watson, and he had his signature squinted-eyes expression, as if deep in thought. The Masterpiece and PBS trademarks appeared at the bottom of the image.
E! News reported that production for "Sherlock" Season 4 started in April 2016 and the show is set to premiere sometime in 2017. Moriarty (Andrew Scott) will return and the story will reportedly be "really dark," according to Amanda Abbington, who plays Mary Morsten. The next season will feature Watson getting ready to become a dad. Aside from Moriarty, there will reportedly be a new villain, to be played by Toby Jones.
International Business Times wrote that the story will again return to Baker Street, where ghosts of the past will haunt Holmes and Watson. Terror and tragedy is coming and the story that was being told from the start is about to reach its climax. The relationship between Sherlock and Watson will allegedly transform after the fourth season.
Steven Moffant, co-creator, writer and executive producer of "Sherlock," mentioned that he still has no idea how long we can keep the momentum going. Personally, he was willing to continue the detective series, although he said that he is hardly the main draw. He would be moderately surprised if he discovers that the fourth season would be the last, but thought that the possibility is there.
Both Cumberbatch and Freeman are quite busy with other projects, although they managed to reunite again for "Sherlock." Moffat said that "Sherlock" can actually go on forever, with the main stars working on other projects and coming back every now and then to do another round.