The final episode of "Sherlock" Season 3 will air Sunday, then it will be back to the game of waiting and speculating about Season 4. The media was abuzz with the news of Seasons 4 and 5 even before the first episode of the current season aired. The buzz started when Benedict Cumberbatch, who plays Sherlock Holmes, alluded to two more seasons of "Sherlock" being in the pipeline.

In an interview to Radio Times in March, 2013, Cumberbatch said: "We've agreed to two more [series] but I could get into trouble for saying that. All I know at the moment is we're doing these three [episodes of Season 3] and another three. I just don't know what there is beyond that."

BBC has yet to officially confirm about "Sherlock" Season 4. It, however, looks like writing has started on Season 4 and themes have been decided. Mark Gatiss and Steven Moffat, creators of "Sherlock," revealed that at a screening of "Sherlock" Season 3 Episode 2, "The Sign of Three."

Gatiss and Moffat came-up with ideas for Season 4 on a train journey. "We always seem to work best on trains," Gatiss said, as quoted by Wales Online. "It was a very strange day... and we mapped out the whole thing in one exciting journey."

"It's some of the best stuff we've ever come up with." The two, however, did not provide a hint of the stories that will make Season 4, which might air in 2015," Moffat said.

Gatiss and Moffat talked about the introduction of Charles Augustus Magnussen in "Sherlock" Season 3 finale. The new adversary will shake things-up.

BBC's Official Synopsis of "His Last Vow": "A case of stolen letters leads Sherlock Holmes into a long conflict with Charles Augustus Magnussen, the Napoleon of blackmail, and the one man he truly hates. But how do you tackle a foe who knows the personal weakness of every person of importance in the Western world?"