After a solid start in the UK, BBC’s Sherlock has grown into a worldwide phenomenon – one that helped launch Benedict Cumberbatch’s film career (not to mention CBS’ modern day Sherlock Holmes TV series, Elementary). In spite of its success, Sherlock remains an event miniseries – with the BBC and showrunner Steven Moffat slowly rolling out one three-episode season every few years.

This winter, the network will be bridging the gap between season 3 (which aired in January 2014) and season 4 (scheduled to premiere sometime in 2016) with a standalone Christmas special – which retains the principle cast but will actually be set in Victorian (instead of Modern) London. Moffat has made it clear that the special will be entirely separate, in order to tell a very specific story, meaning that fans of the series will have to wait until season 4 to discover what’s next for present day Sherlock and Holmes – as well as the source of/reason for Moriarty’s posthumous message.

While the showrunner has remained cryptic regarding where the series will go in season 4, in a recent interview Moffat offered new details about what viewers can expect – teasing a dark and frightening set of episodes that will have Sherlock fans “desperate” for season 5.

We’ve pulled the most intriguing quotes from the interview below – or head over to EW for the full conversation:

The first series was all about the beginning of their friendship. Second about the formative stages, the love and fear and loss and all that. The third was good days, me and my pal and my pal’s wife. Those are golden days. The missing element in a lot of Sherlock Holmes adaptations is allowing it to be funny. There’s a lot of humor in Sherlock Holmes, and it’s ignored in a lot of adaptations. [Season 4] is going to be… I suppose you’d say… consequences. It’s consequences. Chickens come to roost. It’s dark in some ways—obviously it’s great fun and a Sherlock Holmes romp and all that—but there’s a sense of… things… coming back to bite you. It’s not a safe, sensible way to live. It’s hilarious and exhilarating some days, but some days it’s going to be bloody frightening.

[It’s probably more serialized]. A lot of serialization is latent, isn’t it? It’s hidden. Series 3 doesn’t look very serialized, but you look back at how much we’re setting up Mary [Amanda Abbington] to be who she turns out to be. It will be three stand-alone films, 90 minutes each, and an ongoing mystery, as there sort of always is.

[Fans will be] desperate for series 5. We’re certainly going to put them through the mill. It’s going to be more of an emotional upheaval. Hopefully enjoyable and fun, all the things Sherlock must always be. It will be tough at times. Maybe that’s the word? A tougher series.

As indicated by Moffat, while season 3 was less serialized than the prior two episodic trilogies, Mary Watson (and her mysterious backstory) was the primary narrative through-line. It makes complete sense that Moffat and his team would continue to explore the human side of Sherlock through the Watsons but, considering that the pair is comprised of a former assassin and a war hero, there’s also plenty of room to explore larger “consequences.”

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Of course, those consequences could also arise from Holmes and Watson’s “consulting detective” work – which, over the course of nine stories (in addition to countless cases the audience did not see), has left the pair with plenty of enemies. Plus, even if viewers think of recent Sherlock Holmes stories (the Sherlock Holmes movie series, Sherlock, and Elementary) as fun mystery tales, the original Arthur Conan Doyle novels are full of harrowing (and tragic) material.

Still, Moffat has made similar comments before about his other high profile show, Doctor Who, and the tonal differences between seasons were mostly subtle – not necessarily major shifts or game-changing plot beats. Even a darker and more frightening Sherlock season needs to contain the same charm as prior chapters – so its unlikely that Moffat will tip the balance too far into darkness.

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In the source books, the fate of Mary Watson is mentioned only in passing, leaving room for Moffat and the writers to explore an entirely untold chapter in the life of Sherlock and Watson, should a season of “consequences” result in fatal ramifications. That said, the TV series has already taken enormous liberties with the original material (beyond modern cosmetic updates), especially when it comes to Mary, so nothing (and no one) is set in stone.

In the interview, Moffat also promised that season 4 will bring answers – with at least one answer addressing a question that no fans have thought to ask:

There are answers coming to questions which nobody has asked. There’s one thing that no one has really brought up […] We’ve actually set up something, I think—[co-creator Mark Gatiss] and me, we’re very exultant about a little thing we’ve set up that no one is talking about. […] It’s not that we’re being clever. We never know. Sometimes people go mad for one thing we think is quiet trivial and completely ignore something we think is standing right in front of you.

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Viewers will surely be interested to see an explanation for Moriarty’s taped message (which appeared in the closing moments of season 3) but which question have we all forgotten to ask?

NEXT: Sherlock 2015 Special First Look Image

Sherlock will return December 25, 2015 for a standalone Christmas Special – with Season 4 set to air in 2016.

Source: EW