The recently released trailer of "Sherlock" Season 4 has fans on the edge of their seats. "Something's coming," goes the voiceover. "Maybe it's Moriarty, maybe it's not. But something's coming." Whatever it is, lovers of the nail-biting series can hardly wait to find out.

The trailer has more interesting stuff in store, with an unidentified woman confronting the detective, "We brought you back to deal with this, what're you going to do?" On the whole, it looks sinister, and one of the lighter, more endearing, moments involves Mrs. Hudson deflating Mycroft Holmes.

Deadline reports that one of the show's creators Mark Gatiss, and co-stars Cumberbatch and Amanda Abbington all agreed on one thing – that the upcoming season is the darkest that the writers have come up with so far. But, on the plus side, there will be some funnier moments as well. When prompted to drop a heavy clue regarding the fourth season, co-creators Gatiss and Steven Moffat instead gave three names: Thatcher, Smith, and Sherrinford.

While these are sure to spin off several rumours, fans also have something else to ponder about. The new season may well be the last in the series. In an interview with The Telegraph, Moffat reportedly stated, "I don't know how long we can keep it going. I'm personally willing but I'm hardly the main draw. I would be moderately surprised if this was the last time we ever made this show. But it absolutely could be."

One of the most compelling reasons behind the possible termination of the series after this season, if it comes to pass, would be the increasingly busy schedules of the show's two main stars. Martin Freeman, who plays Watson, is already popular on the Hollywood front. Additionally, Cumberbatch's recent entry into the Marvel universe will only take a toll on the filming schedule.

In the meantime, fans can take heart in the fact that neither of the show-runners have issued an official statement regarding the end of the franchise.