The BBC revealed that 'Sherlock' will be returning in 2016, which means the producers are sticking to the pattern of releasing a new season every two years. Additionally, there will be a one-episode special before the new season, which will air in December, 2015.

The exact date of the season premiere, however, is unknown, at least partly because Benedict Cumberbatch and Martin Freeman have extremely busy schedules and getting them together can be difficult (they both play characters in 'The Hobbit' movies, for instance).

Despite the date, there is already speculation about what will happen in the fourth season. One rumor says that Tom Hiddleston, best known for his role as Loki in several Marvel movies, might play Holmes' brother Sherrinford (Mark Gatiss plays another Holmes brother, Mycroft).

The show's producer Steve Moffat has described Season 4 as "devastating," and he hopes it can top Season 3.

"We have a plan to top it. And I do think our plan is devastating. We've practically reduced our cast to tears telling them the plan ... we're probably more excited that we've ever been about Sherlock," Moffat said.

This has led to speculation that a character might die in the upcoming season, but a question remains, who?

Fans can recall that during the third season, Dr. John Watson had married Mary Morstan, who was visibly pregnant by the season's end.

It's a good bet she'll have her child during the fourth season - and fans will watch them and Sherlock adjust to the realities of having a baby in their lives.

Amanda Abbington, who plays Mary, said in an interview, "On the one hand, they'd probably be reckless because they're both quite psychopathic. But I think an assassin and an army doctor who loves trouble, I mean, that kid has got nothing to worry about. Screwed up mentally, of course, but if there's any bullying on the playground, we're covered."

Beyond that, fans can expect romance, as there seems to be two women in Sherlock's life, Molly Hooper and Mart's friend, Janine.