Every coin has two sides, every number an opposite. In the case of Sherlock Holmes, his other half is Professor Moriarty, the shadowy criminal mastermind who serves as the greatest threat to the world's greatest detective -- quite a feat, really, considering that the character directly appeared in only two of Sir Arthur Conan Doyle's original stories.

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But Moriarty is stepping out of the darkness and into the light when "Mad Men" actor Jared Harris fills out his villainous shoes, playing opposite Robert Downey Jr.'s Holmes in "Sherlock Holmes: A Game of Shadows," which arrives in theaters this holiday season. As MTV News' Fall Movie Preview continues, we spoke with Harris about what goes into portraying such an iconic (if often unseen) villain, and all the red herrings and moral ambiguity that come with the package.

MTV: Professor Moriarty is a character with great history in the "Sherlock Holmes" universe and beyond. What kind of research and preparation went into getting into the spirit of the character?

Jared Harris: Well, I tried to hatch some worldwide domination plots. [Laughs] What's interesting is that when he appears in the Sherlock Holmes books, he doesn't appear very much; he's talked about, but you don't see him very often. I thought a little bit about previous incarnations of him. But there were two things that were tricky about this: that convention of who that character was in the Sherlock Holmes stories, this sort of arch nemesis/supervillain. It's been borrowed so often that you can't just go back and do it the way it was, because it seems like a cliché or something. You're only one bad line away from stumbling into cliché in those sorts of things. So we thought about successful villains in other stories and how they operated.

MTV: You've played villains before. How do you make these characters relatable for you? With Moriarty specifically, were you able to dive into him and find a way to like this man?

Harris: You've got to enjoy your work, basically, and you need to have the character enjoy their work as well. I understand what you're saying. You can relate to the character, but it's difficult to always turn around and say you like a character as evil as that. But in my mind, the trick I've played with is, that quality in you and in all of us, when we like or dislike someone, there's a judgment and a moral value involved ... so I removed that from the equation. I don't feel that this guy had any sense of morality. He doesn't see things as right or wrong; he sees things as possible or not possible. From that point of view, the character was liberated and free to do anything.

MTV: Obviously we've already met Moriarty's equal number, Sherlock Holmes, in Guy Ritchie's first film. That version of the character certainly has brains, but he has some brawn to back it up, too. What's your Moriarty like? Is he a similarly multifaceted threat, or is it really his wit that's his sharpest weapon?

Harris: I can't give too much away. It's in keeping with the original version: It's a Guy Ritchie movie, so they haven't suddenly gone back and made a Basil Rathbone "Sherlock Holmes." It's all in keeping with that. But I can't give too much away. Whatever stuff is in the story that they're trying to keep secret until the time comes along, my feeling is it's their secret to blow, and when they feel like blowing it, then I'm free to talk about stuff. That in particular, there are some elements of what you're asking that definitely point to things they've said they'll keep close to their chests until we get closer to [the release date].

MTV: Very interesting! Maybe you can tackle this one a bit more openly -- I imagine that most of your screen time is with ...

Harris: Robert, yes. I loved him in the first movie, and I have even more respect for him now. I found him to be very generous and attentive. He wants people around him to do their best work. Sometimes you run into these things where people aren't like that, maybe they're insecure. He's not insecure about talent at all. He wants other people to raise their game. I loved it. I really enjoyed working with him. I can't say enough highly about him. I think he's very special.

MTV: Fans are very eager to see the way you bring Moriarty to the big screen. There have been a lot of eyes on this character, from even before his brief appearance in Ritchie's first "Sherlock" movie. Do you feel any sort of pressure to live up to a certain expectation of this character?

Harris: I certainly didn't ignore that. There are a couple of ways we talked about how you handle that. But he's a very famous character, an infamous character. The man's name is really well known. But it's interesting, because like I said, he only actually appears in two Sherlock Holmes stories. The rest of the time his reputation is done wonders by Sherlock Holmes; he talks him up a great deal. You kind of want to play on that element. It's similar to ... a monster movie; the real thought of the monster movie is you don't reveal the whole shark until the very end of the story. You want to keep people guessing as much as you can, and not show too much, while throwing in a few red herrings and stuff like that. I have no idea, because I haven't seen it, how much it works. [Laughs] But you are very conscious about all that.

At the same time, it's a very different "Sherlock Holmes" film. It isn't a very traditional Sherlock Holmes story at all. It does maintain a truth to the spirit of the times and very much the idea of what we have of Sherlock Holmes and his stories as filtered through this Victorian ideal of how these people behaved and everything, but those were rough, rough, rough times. I wouldn't be surprised that if you went back in a time machine, you'd find that it's actually much closer to what Guy Ritchie is doing than what the Basil Rathbone ones were doing, where everyone's extremely polite with all their clothes pressed and everyone's clean all of the time. I would imagine that! I remember reading at school that Queen Victoria took a bath once every six months and that was considered outrageous, that she was very clean and she was overdoing it.

From "Abduction" to "Muppets, "Moneyball" to "Breaking Dawn," the MTV Movies team is delving into the hottest upcoming flicks in our 2011 Fall Movie Preview. Check back daily for exclusive clips, photos and interviews with the films' biggest stars.

Check out everything we've got on "Sherlock Holmes: A Game of Shadows."

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