'Sherlock' Season 4 Special Screening: What Happens In 'The Six Thatchers'? Get The Details! [SPOILERS]

"Sherlock" had a special holiday screening of the first episode of Season 4 at the London's Ham Yard Hotel recently. The cast members, led by Benedict Cumberbatch and Martin Freeman, were in full attendance.

The first episode entitled "The Six Thatchers" was well-received by both audience and critics. So, what can fans expect to see when it airs on Jan. 1 on TV?

According to Den of Geek, "Sherlock" Season 4 will start of light with humor, fun and action as Sherlock Holmes (Cumberbatch) and John Watson (Freeman) find clues to solve their case. But the tone will turn dark in the episode's next half.

Co-creator Mark Gatiss did say in an old interview with Entertainment Weekly that the new season of "Sherlock" will be a "frightening, tough, emotional upheaval." It will also emphasize on consequences, which quickly comes to a blow in the first episode, as the reviews have noted.

On a lighter note, John and Mary Watson have become parents in "Sherlock" Season 4. Their baby's name - Rosemary Mary Watson -- has been revealed in an actual birth announcement that was published on Telegraph. It is believed that the baby's arrival will have an effect in the relationship of Sherlock and Watson.

With Watson's family expanding, Sherlock will not be completely alone, though. He has a new companion in the presence of a bloodhound. The dog will provide a much-needed comic relief in "The Six Thatchers."

The first episode of "Sherlock" Season 4 takes inspiration from author Sir Arthur Conan Doyle's "The Adventures of the Six Napoleons." It is about a military leader's plaster bust that was destroyed to reveal a hidden object.

"Sherlock" Season 4 premieres on BBC on Jan. 1 in the U.K. For American viewers the show will air on PBS. Meanwhile, the final episode of the series, "The Final Problem," will be running in select U.S. theaters on Jan. 16 through 18. Watch the teaser of the latest "Sherlock" in the video below.