It's almost cruel to report on Sherlock season 4 and the upcoming special when they're so far away.  As we previously reported, a Sherlock "Christmas Special" is due out in December 2015, and it will be followed by three new episodes.  Filming on the special is set to begin in January with filming on season four happening later in the year, and the show's co-creator Mark Gatiss told Britain's Radio Times that "you can always expect tragedy as well as adventure," although I'd say each season is fairly short on tragedy until the finale.

But fans of Sir Arthur Conan Doyle's novels may already sense where the tragedy in season four might come in.  Hit the jump for more, but be warned that if you're unfamiliar with the books, and/or if you don't want to know about the return of Moriarty (Andrew Scott), there are spoilers ahead.

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Image via PBS 

If the show sticks close to the books, then fans know that Mary Watson (Amanda Abbington) dies, and that could be the "tragedy" Gatiss is referring to.  However, Gatiss tried to at least offer the possibility of Mary living by telling Radio Times [via Variety]:

"Just because it’s in the stories doesn’t mean it’ll happen in the series because there’s an awful lot of changes and an awful lot of places to go and things to do." He added, "It should be clear by now that while, of course, Doyle is our absolute god, we have gone quite a long way away as well… so there are lots of surprises to come."

One such departure from the in the novels is that when Moriarty died in The Adventure of the Final Problem, he stayed dead and never reappeared in Holmes' life.  Moriarty could still be physically dead in Sherlock, but that didn't stop him from coming back in the season three finale, and taunting Sherlock, "Miss me?"  (My theory: Moriarty's new incarnation is a computer program).

While Moriarty remains Sherlock's most notorious and powerful nemesis, Gatiss says that this mystery will be "completely" cleared up in the special, and that season four will tackle new adventures.  But as to whether or not you can really keep Mortiarty down, Gatiss added, "Well, it’s very hard to put a lid on Andrew Scott…"

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