For BBC's "Sherlock" season 4, creators Steven Moffat and Mark Gatiss gave fans these clues - Thatcher, Smith and Sherrinford, which will be the themes for the upcoming three-episodes fourth season. There have been widespread speculations what the clues could mean, but perhaps the biggest draw that fans are anticipating is a Sherlock (Benedict Cumberbatch) and Irene Adler (Lara Pulver) reunion on screen.

Cumberbatch plays the modern-day detective in "Sherlock," which has a huge following in Britain and the United States. Fans are highly anticipating season 4 after a three year hiatus, not including the Christmas special, "The Abominable Bride," which aired in January of this year.

Moffat and Gatiss draw their stories from Sir Arthur Conan Doyle's "Sherlock Holmes" detective stories. Hence, the first episode of the show, "The Six Thatchers," is more likely to be based on Doyle's "The Adventures of the Six Napoleons."

Dr. John Watson (Martin Freeman) recounts the Thatcher story in his official blog, a spin-off for the show. The case is straightforward with Sherlock himself saying that it is very simple, but fans know that there will be plot twists in the story that will introduce another nemesis as insane or even more perverse as Moriarty.

The BBC teaser trailer gave fans a look into a very dark, almost frightening "Sherlock" in season 4. Moffat in an interview with Entertainment Weekly calls season 4 as a "tougher series," putting both Cumberbatch and Freeman in etxra challenging roles.

This could be attributed to the coming of Culverton Smith (Toby Jones), whose character in the book tries to poison Sherlock with the use of tropical diseases. "Sherlock" episode 2, "The Lying Detective," could mean that Sherlock will have to lie or pretend to be dying in a bid to catch Smith in his crimes.

Sherrinford Holmes may also make an appearance and lay truth to Mycroft's outbursts referring "to the other one" meaning a long-lost sibling. Tom Hiddleston is rumored to play the part after being seen posing with Gatiss in the San Diego Comic Con as reported by Digital Spy. Gatiss then posted the picture to twitter with the caption "blud," a word Sherlock used for Mycroft.

Another persistent rumor is the Sherlock and Irene Adler reunion, which started way back in season 2, episode 1 "A Scandal in Belgravia." Rumor has it that it will be Irene who will save Sherlock from the clutches of Smith.

All these clues will be revealed as "Sherlock" season 4 premieres on Jan. 1, 2017.