Comic-Con: 'Sherlock' Team Teases "Darkest" Season Yet — Watch the Season 4 Trailer

Sherlock Still - H 2015
courtesy of Photofest

"We're not saying anything."

Although executive producer Steven Moffat was extremely tight-lipped about the upcoming fourth season of Sherlock, the team behind the beloved drama still made a splash Sunday at Comic-Con.

Moffat was joined by stars Benedict Cumberbatch — in his first Comic-Con appearance for the series  and Amanda Abbington as well as executive producers Mark Gatiss and Sue Vertue to discuss what will be the show's first new season in three years.

With the exception of last year's Victorian Christmas special The Abominable Bride, Sherlock hasn't released new installments since 2014. Hundreds of fans starved for information and footage from season four went so far as to sleep outside of Hall H Saturday night to ensure they made it into the panel. (Cumberbatch visited some of the fans Saturday night and thanked the crowd for a "humbling" reception at the panel.)

Although the panel was light on spoilers, the team unveiled the first season four trailer. The lengthy video, which teased that "everything they know will be tested," elicited cheers, gasps and thunderous applause from the room.

Premiering in 2017, season four will consist of three 90-minute episodes and feature new addition Toby Jones, who can be seen in the trailer. "It's really dark. It’s the darkest that Steven and Mark have written," Abbington said. "When we read them, all of us, we were kind of overwhelmed by them because they were shocking and amazing as always."

Cumberbatch teased "quite a few tears" in the new episodes. "It's a genuine emotional roller coaster," he said. "The learning curves, they're massive."

Part of the reason for the delay has been the actors' busy schedules. Cumberbatch is next set to headline Marvel's Doctor Strange "Sherlock is a lot more effing strange than Strange is," Cumberbatch said  and Martin Freeman has gone onto TV projects like Fargo season one and Crackle's StartUp.

"We just don’t make very many," Moffat said. "We're always fresh and rested when we make a new series."

Because of the delay, and that scheduling difficulty, the executive producers said they work hard to make sure the resulting episodes are much more than just an episodic crime drama. "We just try very hard over the last six years to keep it evolving," Gatiss said. "You have to put the characters through an emotional wringer."

Cumberbatch praised how the character has changed since the series began. "There's an evolution to all the characters and that as an actor is a pleasure to play," Cumberbatch said. "The level of reinvention and the sheer ballsiness of it; what we're doing now is so ambitious."

Cumberbatch said that evolution also extends to Sherlock's relationship specifically with Mycroft in season four. It's "an evolving relationship," the actor said. Added Gatiss: "A lot of things are resolved. A lot of things are raised."

Moffat spoke to the evolution of the character in the original books as well. "The Sherlock Holmes at the end of the story is not the same Sherlock Holmes you meet at the beginning," he said. "You can't do a show about a genius who doesn’t learn."

One thing that won't change? Sherlock's signature style. "So long as Benedict always wears the coat, and we never change the coat," Moffat said with a laugh.

With shooting set to wrap on season four in two weeks, questions in the panel turned to the future. Will there be a fifth season? Or will season four will be the last.

"We have no idea whether it will be the last one or not," Moffat said. Added Gatiss: "We always hope to carry on. Everyone loves the show."

Asked specifically about the cast returning for season five, Moffat had a little fun with his response. "Why is everybody assuming they survive season four?" he said with a laugh. "We told you it was dark."

Sherlock returns to PBS' Masterpiece with new episodes in 2017. Watch the trailer below: