'Sherlock' Co-Creator Teases "Major, Life-Changing" Season 4 Ahead of Christmas Special

The Sherlock Christmas special has yet to air, but co-creator Mark Gatiss is already jumping ahead and teasing Season 4 of the hit BBC show based on Sir Arthur Conan Doyle's classic mystery stories. In an interview with Entertainment Weekly, Gatiss, who also writes for Doctor Who and portrays banker Tycho Nestoris on Game of Thrones, teases the "major, life-changing" upcoming season.

"I just finished [writing] episode 1," Gatiss told the outlet when asked how the new season is going. When teased for more details, he says, "Well it's more adventures! 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."

Fans of the Benedict Cumberbatch- and Martin Freeman-starring show will remember that the end of Season 3 seemed to hint at Moriarty's (Spectre's Andrew Scott) return to the show.

The buzzy season will reportedly start filming later next year, with a rumored air date of 2017. According to co-creator Steven Moffat, the long wait in between seasons (which is usually two years, but in the case of Season 4 could stretch to three or more), is due to the fact that "Benedict and Martin became big stars," adding that the show is "worth waiting for and it makes it a special event."

To whet fans' appetites, a 90-minute Christmas special of the show is airing Jan. 1, 2016. The episode, titled "The Abominable Bride," will feature the famous crime-solving duo (and friends) in the Victorian era, when Sir Arthur Conan Doyle's stories were originally set.

According to the creators, despite the special being set in the Victorian era, Season 4 will pick up where Season 3 left off: in modern times.

"The Abominable Bride" airs in the U.S. on Jan. 1, 2016 at 9 p.m. ET on PBS. It will also air in the U.K. on the same day, a first for the series.