Episode 2 of Sherlock Season 4 premieres this week. And fans are wondering what will happen in "The Lying Detective."

Sherlock Season 4, Episode 2 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 Lying Detective" online this week via the PBS/Masterpiece website.

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Last week on Sherlock Season 4, Mary (Amanda Abbington) died after taking a bullet for Holmes (). But while fans were shocked, showrunner Steven Moffat said that Mary was never going to be around for very long.

Watch the Sherlock cast and crew discuss Mary's death in Season 4.

"The reality of this, of course, is that Sherlock Holmes is about Sherlock and Dr. Watson [] and it’s always going to come back to that — always always always," Moffatt said after last week's Season 4 episode. "They had fun making it a trio but it doesn’t work long term. Mary was always going to go and we were always going to get back to the two blokes. That’s the format. [Producer-actor] Mark Gatiss and I do not have the delusion that we know better than Sir Arthur Conan Doyle. That’s how the show works and always will."

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But things won't got back to normal so easily on Sherlock Season 4. At the end of last week's premiere, Watson blamed Holmes for his wife's death.  And we will reportedly see a different side of Watson in the rest of the season.

"It’s always interesting to play shades of people," Freeman said after the Sherlock Season 4 premiere. "John is this reliable, steadfast character generally speaking. But he has weaknesses and can be at fault."

Watch behind the scenes footage from Sherlock Season 4

So what will happen on Episode 2 of Sherlock Season 4? Spoilers say that "The Lying Detective" will feature a new villain named Culverton Smith (). Smith initially appeared in Doyle's short story "The Adventure of the Dying Detective," which many think is the inspiration for this week's episode.

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"This guy is the purest evil," Moffat said of Smith before "The Lying Detective." "Sherlock is actually appalled by him. He’s the most evil villain we’ve had. I don’t think that when you see it, you will disagree. He’s horrific."

Watch a preview of Sherlock Season 4, Episode 2, "The Lying Detective."

Smith actually made a brief appearance in the Sherlock Season 4 premiere. A poster for Smith's TV show was in a scene between Watson and Elizabeth (Sian Brooke), Watson's possible mistress. So some are wondering if Elizabeth is actually connected to Smith in some way. If so, we may find out more about her character in Episode 2.

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