While fans eagerly await the Christmas special for the television show "Sherlock" entitled "The Abominable Bride," co-creator Mark Gatiss is already teasing about what is in store for season 4.

"I just finished (writing) episode 1," Gatiss told Entertainment Weekly.

To recall, when the third season of "Sherlock" wrapped up, Sherlock Holmes' (Benedict Cumberbatch) most formidable enemy James Moriarty (Andrew Scott) seemed to have come back to torment the super sleuth.

With the return of his archenemy, Gatiss was asked what will happen to Sherlock. Without giving too much spoilers away, Gatiss revealed that great things are in store for the main characters.

"Well, it's some more adventures. Ha ha!" he laughingly said. "All I can say is, this is a major, life-changing series for the regulars. The repercussions of Moriarty's apparent return are far-reaching. It's very big stuff."

In an earlier interview, Gatiss talked about the possibility of a "Doctor Who" and "Sherlock" crossover. His co-creator Steven Moffat, who is also the lead writer and executive producer of "Doctor Who" was all for it. Moffat said that he would love nothing better than to see this develop; however, he is facing some opposition from his fellow collaborators.

One such person is Gatiss, who insist that merging the two world makes absolutely no sense. He is so against the mash-up that he said it will only happen "over my dead body."

"I'm not being horrible but I just don't see the point," he said. "First of all, they are entirely different shows. But I think there'd be so much excitement among certain members of the fan community followed by massive disappointment that it wasn't the version they had in their heads. And, just personally, I've never been (a) fan of these kind of mash-ups."

What makes "Sherlock" such a big hit, according to the co-creators is that the character of Sherlock is very complex. Even though he is quite arrogant and mean, people still adore him for his brilliance.

"The big thing about him is he's famously very good with women, he can be very charming, but, as it says in the original stories, he's very abrupt, he's very rude. There's a huge thing when they first meet when Watson says, 'this fellow may be very clever but he's certainly very arrogant' and it's all the same," Gatiss told Den of Geek.

"The Abominable Bride" will air on January 1, 2016 at PBS.