The Sherlock Season 4 premiere date is on New Year's Day. And fans are wondering what will happen in Episode 1, "The Six Thatchers."

Episode 1 of Sherlock Season 4 airs in America Sunday on PBS at 9 p.m. ET. And if you can't get to a television, you can also watch "The Six Thatchers"  online this week via the PBS/Masterpiece website.

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The synopsis for "The Six Thatchers" states that Sherlock () will return to England as Watson () and his wife Mary () prepare to welcome their first child.

Watch a preview of the Sherlock Season 4 premiere.

"The baby is a mystery to [Sherlock], and he’ll be slightly befuddled when things don’t go according to logic, because babies don’t do logic!" co-creator Mark Gatiss said before Episode 1 of Season 4. "So he treats her as a sort of problem to be solved rather than an emotional issue. It’s a bit like the best-man speech from last season. He treats it like a case, like it’s 'The Puzzle of the Child.'"

Ironically, Freeman and Abbington just announced their breakup after 16 years together. The split took place just two weeks before Season 4 began filming.

"[It was] so weird, especially playing new parents again, up all night feeding and things, because we were effectively revisiting how it was when we first got together," Abbington said before the Sherlock Season 4 premiere. "I love working with Martin, and we definitely would do again, but there were some pressure points in this episode where we thought, ‘oh, are we doing the right thing here?’, but the resounding answer was always yes."

"The Six Thatchers" synopsis also reveals that Sherlock will spend much of the Season 4 premiere trying to figure out Moriarty's next move. When someone starts destroying images of Margaret Thatcher, Sherlock will wonder if the crimes are connected to something in Mary's past.

Watch Abbington discuss her character's past before Episode 1 of Sherlock Season 4.

"What’s very exciting about these three episodes is to really play the repercussions of the last season," Gatiss added before Episode 1 of Sherlock Season 4. "There are lots of things that come to fruition this season which we have been seeding for a while. We knew we were going to get here. And, with the things that we’ve been planning, the darkness was sort of inevitable. They’re not things that could have happened any time, and where we get to is a very different place to where we’ve been before. He said, elliptically."

What do you think will happen on Season 4 of Sherlock? Let us know your take in the comments section below!