Series creators Steven Moffat and Mark Gatiss confirmed that "Sherlock" season 4 will return with a much darker story. Jim Moriarty (Andrew Scott) is also expected to come back and haunt Sherlock (Benedict Cumberbatch) in the upcoming season.

At the San Diego Comic-Con last July, Moffat and Gatiss, along with Cumberbatch, went into detail about what fans can expect from the upcoming season 4 of "Sherlock." They also described what makes Sherlock himself and how his personality has evolved.

"Sherlock" season 4 is expected to be the darkest season of all. Cumberbatch described the upcoming season as, "Myopically dark. You're talking about the end of the universe darkness. You can't see in front of you and would walk into everything dark." Reasons for the season's presumed darkness could be revealed in the season premiere.

One thing that will never change about Sherlock is his favor of reason over emotion, says Moffat. Although Sherlock has learned to become understanding of his emotions, he would hate to become like everyone else.

"He becomes more human and more adept at fitting in with a lot of people, but he remains separate from the human race because he finds that a better place to observe that from. He stays on the mountaintop because there, he can see clearly. But he stays on the mountaintop, and he will die up there. He's not going to change that," Moffat explains.

Parent Herald reports that Sherlock will push himself to isolation in season 4, to prevent his enemies from succeeding with their plans to eliminate him. Although this is the best solution for Sherlock because he runs with reason, this will cause John Watson (Martin Freeman) and Mrs. Hudson (Una Stubbs) to feel pained and helpless for not being able to save Sherlock from himself.

Lifestyle reports that Moriarty will be returning in "Sherlock" season 4. The episode premiere will open with Moriarty's voice saying, "Did you miss me?" It seems that Sherlock's arch nemesis is not done with terrorizing the consulting detective.

Besides Moriarty, another villain will be introduced in the upcoming season. Culverton Smith (Toby Jones) will be the new villain in "Sherlock" season 4. The said villain will have terrible teeth and will prove to be the darkest villain yet of the series.

"Sherlock" season 4 premieres early in 2017.