Earlier this year, BBC network has announced a tentative 2016 air date for the fourth season of the popular detective series, 'Sherlock'.

Additionally, It was also reported that there might be a 'Sherlock' episode that will air prior to the start of Season 4.

'Sherlock' actor Martin Freeman, who plays Dr. Watson in the series, first hinted that about the idea of a spin-off special.

"Mark Gatiss may beat me up, but there is an idea for this one-off special that's such a good idea," Freeman said, "Chatty Man."

Freeman added that while the idea was discussed, he does not know when it's going to happen.

"As I was listening to it, I thought 'we've just got to do this.' It's a fantastic, really mouth-watering idea. But I really don't know when we are going to get to do it," added Freeman.

Although the actual air date for the show is still unknown, a lot of speculation about the plot for the fourth season has been circulating.

Plot rumors about Season 4 include theories on Moriarty coming back, and an introduction of a third Holmes brother.

Moriarty's reappearance after he died in the show last season triggered rumors that the character might still be alive, and be back for the next season.

However, Steve Moffat, a writer for the series, denied the possibility of Moriarty's comeback in the upcoming season through an interview with IGN.

"He can't come back from that. He shot himself in the face. What more do you want?," said the writer.

As for the introduction of the third Holmes brother, the rumor began earlier this year, when Mark Gatiss, the show's creator, said that he would love the idea of 'Thor' actor Tom Hiddleston as the brother.

"Tom would be wonderful in Sherlock, I'm sure, but he only does movies now. What can I say?," said Gatiss.

Meanwhile, the Moffat stated that the team is brewing something devastating in order for Season 4 to 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 told E! News.

The writer revealed that the team is trying to direct the show toward somewhere they've never been before.

"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," added Moffat.