Sherlock and Watson are back in the game once again! Fans of the hit TV series would be delighted to know that their favorite sleuth is back in action and ready to solve mysteries once again.

According to the tweet by BBC, fans of the show will be treated to a heart-stopping one-episode special before the fourth season. According to a report by TV.com, filming for the show has officially started. The site has also speculated that the one-episode special will be premiering at around Christmas time and that the fourth season will have a 2016 release date.

There has also been some speculation as to what mysteries the detective from Baker Street will be encountering in the new episodes. Around 80 years ago, a lost Sherlock Holmes mystery written by Sir Arthur was discovered. Will this lost story be part of the new season, or be incorporated for future seasons? 

"Of course, it's far too early to say what's coming, but we're reasonably confident that the very next thing to happen to Sherlock and John, is the very last thing you'd expect ... " said show creator Steven Moffat.

According to Moffat, the upcoming season will be "better than season 3, with 'darker' storylines". 

"We have a plan to top [Season 3]," teased Moffat. "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."

"It will be challenging place to go. We always start with a re-introduction that builds toward a darker climax - we might just be going darker [from the outset]. We got a very, very good set of ideas." he added.

Fans will also be seeing Watson as a father, and it is teased that he and Mary will make for 'interesting parents'. "On the one hand, they'd probably be reckless because they're both quite psychopathic," said Amanda Abbington, who plays Mary in the show. "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."

The fourth season was also teased to be "devastating". Will this end up in Mary's death? Also, what will the special be all about? According to some teasers, the special will most likely wrap up the Moriarty mystery. There was also a teaser picture on Twitter which involved a quote from Sir Arthur Conan Doyle's The Adventure of the Blue Carbuncle.

Are you excited for Sherlock Season 4?