With the possibility that the fourth season of BBC's Sherlock could be the show's last, the team is pulling out all the stops to make sure that their loyal fans would get more than what they expect from the season.

Showrunner Stephen Mofatt said that fans should be open to the possibility of ending the series after series 4 because of the busy schedules of its two lead cast members. Aside from landing plum roles in Hollywood films, Benedict Cumberbatch has been attached to blockbuster franchises like the Star Trek reboot, the Lord of the Rings and most recently, cast as Doctor Strange.

Martin Freeman has enjoyed being the lead of the Hobbit trilogy and has now landed a multiple picture deal with the Marvel Cinematic Universe in what promises to be a lucrative role which remains secret until now.

In an interview with Collider, Sherlock himself hinted that the upcoming season will be extremely dark with a looming sense of danger for Sherlock and his good pal Dr. Watson.

The season is expected to introduce villain Culverton Smith, who will be played by talented actor Toby Jones, an antagonist that showrunner Stephen Moffat promises would be Sherlock and Watson's biggest challenge.

"He's completely different [to the villains that have come before]. It's a completely different character. He's the darkest villain we've had. There was always something charming and engaging about Moriarty. There was something fascinating and actually amoral, rather than immoral, about Charles Augustus Magnussen. This guy is the purest evil. Sherlock is actually appalled by him. He's the most evil villain we've had. I don't think that when you see it, you will disagree. He's horrific," he explained.

No official air date has been confirmed yet but based on trends set by initial seasons, it could premiere as early as January 2017.