BBC has released the official trailer of the fourth season of "Sherlock." Unveiled to the audience at the San Diego Comic-Con and subsequently posted on YouTube, the video sees tons of action and teases the possible return of Moriarty.

"Something's coming. Maybe it's Moriarty, maybe it's not. But something's coming," Sherlock's voice narrates at the beginning of the clip. The general vibe of the video is ominous and dark, which is what the producers of the show are going for.

"It's the darkest that Steven and Mark have written...If we can pull this off, it will be amazing," Amanda Abbington, who plays Mary Morstan, teased of the upcoming season. "It's a genuine emotional roller-coaster," Benedict Cumberbatch, who plays the titular Sherlock Holmes, continued.

As for what or who will cause their worlds to turn upside down, it is widely believed that it will be none other than Andrew Scott's Moriarty. However, as Sherlock pointed out, it may not be him. It remains to be seen exactly what or who they will be dealing with in the fourth season, but one thing is for sure: It's going to spark a lot of action sequences.

The video itself, which spans for a minute and a half, features guns ablaze and even an explosion. Moreover, teaser texts reveal that "everything they know will be tested" and "everyone they know is under threat."

It is certainly looking like season 4 is one to watch. Co-creators Mark Gatiss and Steven Moffat, along with producer Sue Vertue, gave out three names in anticipation of the new season: Smith, Thatcher, and Sherrinford. 

Could these be new characters? Deadline posits that Sherrinford is another Holmes brother, pointing out that the name was originally considered by author Arthur Conan Doyle for the lead protagonist before ultimately deciding on Sherlock.

At this point, fans can only wonder and theorize. Only time will tell who these characters are and what mystery will envelope the fourth season.

"Sherlock" season 4 will premiere in 2017.