For the audience in UK, It is time to say goodbye to "Sherlock" on Sunday. The promise of cracking Season 4 and Season 5 is likely to keep the millions upon millions of "Sherlock" fans in good spirit.

The writing duo of Sherlock, Mark Gattis and Steven Moffat, have shed this cloak of secrecy and are freely talking about the two new seasons. At the BAFTA screening of "Sherlock" Season 3 final episode, "His Last Vow," Gattis and Moffat said that they have come-up with some of the best ideas for Season 4 and Season 5 of "Sherlock."

"Rather excitingly, Mark and I, for no particular reason, we just got out of the rain and sat at the top of the [Sherlock] production bus... and we just started plotting out what we could do in the future," said Moffat, as quoted by Radio Times.

Moffat also revealed that they have plotted out the entire Season 4 and Season 5, saying: "The ideas we had that day, I thought were the best we've ever had."

Talking about their process of coming-up with ideas, Moffat said that their writing plan does not include blowing-up the world or casting a world famous personality. Sherlock's writing duo plans tend to be more about "What exciting twists and turns can we add to this?' And I think we've got some crackers!"

Previously, Moffat and Gattis had talked about Season 4 after the screening of "Sherlock" Season 3 Episode 2, "The Sign of Three." We always seem to work best on trains," said Gatiss, 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," added Moffat.

On Sunday in the season finale of "Sherlock," the new terrifying adversary of "Sherlock" will be introduced. He is Charles Augustus Magnussen, the one man that Sherlock hates and after the reunion and the wedding time, it is likely the time for tears as this new chilling villain is going to shake things-up.