Sherlock season 4 will be 'life-changing' for characters, says Mark Gatiss

Sherlock fans have yet to see the Victorian era-set special Christmas episode of the sleuth show, but co-creator Mark Gatiss is already hard at work on the next season of the Benedict Cumberbatch- and Martin Freeman-starring update of Sir Arthur Conan Doyle’s classic detective tales. “I just finished [writing] episode 1,” reveals Gatiss, who is also a regular writer on Doctor Who and plays the banker Tycho Nestoris on Game of Thrones.

The third season of Sherlock screened back at the start of 2014 and ended with the seeming return of Sherlock Holmes’ archenemy Moriarty, played by Spectre star Andrew Scott. Can Gatiss say anything else about the upcoming season of the show, which is set to start shooting later next year? He can! “Well, it’s some more adventures. Ha ha!” chuckles the writer. “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.”

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You can see the new trailer for the special Christmas episode of Sherlock below. “The Abominable Bride” airs Jan. 1 as part of PBS’ Masterpiece strand.