• Benedict Cumberbatch (L) and Amanda Abbington attend the 'Sherlock' panel during Comic-Con International 2016 held on July 24, 2016 in San Diego, California.

Benedict Cumberbatch (L) and Amanda Abbington attend the 'Sherlock' panel during Comic-Con International 2016 held on July 24, 2016 in San Diego, California. (Photo : Getty Images/Kevin Winter)

A release date for "Sherlock" Season 4 has officially been confirmed, and with that, spoilers and plot details abound. The show continues the journey of Sherlock (Benedict Cumberbatch) and Dr. Watson (Martin Freeman) as they face possibly the darkest season yet.

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"Sherlock" Season 4 sees the rise of Culverton Smith, played by Toby Jones. The new villain is said to be the darkest the show has ever had, even eclipsing the terrors brought by previous villains such as Moriarty and Charles August Magnussen.

"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," The Independent  quoted the executive producer Steven Moffat as saying.

"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," Moffat added.

Despite the dark tone of the upcoming season, Dr. Watson and his wife Mary will be providing some of the lighter, warmer aspects of the story. The couple are expecting their first child in the fourth season, which means Sherlock is going to be an uncle.

There are also rumors that "Thor: Ragnarok" star Tom Hiddleston will star as Sherlock's mysterious brother.

To many of its fans, the fourth outing of "Sherlock" is a long time coming. However, there are rumors that this would be the last season for the show. In an interview with British GQ, Cumberbatch hinted that wrapping up filming for "Sherlock" Season 4 felt like "the end of an era."

"It might be the end of an era. It feels like the end of an era, to be honest," Cumberbatch shared. "It goes to a place where it will be pretty hard to follow on immediately. We never say never on the show."

Cumberbatch added that while he would want to revisit the show and reprise his role as Sherlock in the future, there is already a feeling that they have made something "very complete as it is."

"Sherlock" Season 4 will premiere on Jan. 1, 2017 on BBCOne.