'Sherlock' season 4 release date, spoilers news 2016: Everything fans need to know about detective story's 4th installment

Production has wrapped up for "Sherlock" season 4 last Aug. 5, but the classic detective story will not be back on air until January 2017. That said, what could fans expect from the upcoming installment?

Up until recently, fans thought Jim Moriarty (Andrew Scott) died on the special episode titled "The Abominable Bride." However, the official trailer for "Sherlock" season 4 opens up with Moriarty uttering a creepy greeting. Check out the video below.

Season 4 will also see a villain worse than Moriarty. Toby Jones will play Culverton Smith, the terrible villain from Sir Arthur Conan Doyle's original Sherlock Holmes tale, "The Dying Detective." The title of the tale itself is foreboding, which is leading many to assume that Culverton's appearance in "Sherlock" season 4 will mean the death of the beloved detective. In fact, there was a part in the story where Culverton took delight watching Sherlock (Benedict Cumberbatch) die after the latter fell sick due to an underhanded scheme the former pulled on him.

Several on-set photos leaked online showed Cumberbatch with a fuzzy, four-legged friend. The addition of the Bloodhound could mean parts of season 4 will be taken from Doyle's second novel, "The Sign of Four," in which Sherlock borrowed a dog named Toby to help him track down a pair of thieves.

There are also rumors that Tom Hiddleston is being tapped to play Sherlock's other brother, Sherrinford Holmes. Creator Mark Gatiss', who also plays the detective's known brother, Mycroft, tweeted a photo of him, Hiddleston, and Amanda Abbington, who plays Mary Morstan, taken at the San Diego Comic-Con (SDCC). He captioned the Instagram photo "Blud," leading some to speculate that the "Avengers" actor's casting is in the works.

The three key words for "Sherlock" season 4 likewise fortify fans' assumptions that Hiddleston will play the third Holmes brother. The keywords released after the show's SDCC panel were Thatcher, Smith, Sherrinford.

Thatcher could be a nod to "The Six Thatchers" that documents Sherlock's escapades, Smith is obviously referring to the big bad of season 4, and Sherrinford is the third brother's name. Fans are hoping Hiddleston will indeed breathe life to the character.

"Sherlock" season 4 is expected to drop in January 2017 on BBC.