The January 1 Sherlock special "The Abominable Bride" established that Moriarty is really dead, while the next season is expected to be darker and more emotional.
According to a report by Crossmap, the last episode of the third season had Mycroft Holmes saying, 'The other one." This could mean that there is another Holmes brother. Reports are coming in that it could be played by famous Loki actor, Tom Hiddleston.
Meanwhile the Christian Post reported that co-creator Steven Moffat hinted that the next season will be dark, "hilarious and exhilarating," and even "bloody frightening." He also said that the fourth installment is "going to be more of an emotional upheaval." Moffat said he expects films to start rolling in April, which probably means that fans will see the next time Cumberbatch play the role of Sherlock Holmes in 2017.
Mashable wrote that "The Abominable Bride" special Holiday episode was a smooth transition that moves the plot forward seamlessly. It connects the Sherlock in the present day and the other story in the 1800s.
One important fact confirmed about the upcoming Sherlock 4 is that Benedict Cumberbatch's Sherlock and Martin Freeman's Dr Watson will go back to the Victorian Era. However, Mark Gatiss said this timeline will only be for the Holiday Special, and has nothing to do with the entire season. Moffat said, "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."
People expected Sherlock 4 to be out in 2015, but Moffat announced that "Sherlock Holmes Season 4" will start production mid-year 2016. This means the release date for the fourth installment will be on 2017. There are talks that Mary could die to childbirth. Martin Freeman hinted that she actually might die, but Gatiss said otherwise.
