Natalie Dormer Natalie Dormer

In the Sherlock Holmes canon, his archnemesis, Moriarty, has always served as a potent stimulant: an intellectual equal who can challenge the master detective's powers of deductive reasoning with his own acts of evil genius. But with the revelation at the end of Elementary's first season last May that Moriarty and Irene Adler (Natalie Dormer) — Sherlock's long-lost lover — were one and the same person, Jonny Lee Miller's Holmes experienced a whole new kind of stimulation.

"They have an incredibly profound connection," says Dormer. "They identify with each other in a way that no other human being on the planet ever has before. At first it was to Sherlock's detriment, and then it turned on its head and it was to her detriment."

Last we heard from Irene/Moriarty, she was in federal custody but still poison-penning love letters to Sherlock. In Thursday's episode, she reappears as a person of interest in a girl's kidnapping. "Sherlock and Joan [Watson, played by Lucy Liu] come to believe that Moriarty might have been involved," says creator Robert Doherty. "She may have even orchestrated the abduction."

As always with these characters, there's a twist: Irene/Moriarty ends up assisting on the case. "It seems it would be to the investigation's benefit to take on her knowledge in this area," says Dormer. "She very cleverly works the situation to her advantage."

It's this ability to play both the ingénue and the antagonist that initially convinced Doherty to cast the 31-year-old British actress in the dual role. "The first series I saw her on was The Tudors, and I loved her look and performance and saw a lot of range there," he says. "She's a great villainess, but she can play the other side of that coin easily."

Dormer didn't know initially that she'd be playing both sides. "I took the job on the premise that I was Irene Adler," she says. "Then it was revealed to me that I was going to be Moriarty, and that was the icing on the cake. There's such a rich heritage — Orson Welles played Moriarty on the radio and Laurence Olivier played him on film — so to be the first incarnation of Moriarty as a woman is very exciting."

No wonder the actress carved out time in her insane schedule — she also costars in Game of Thrones and will join The Hunger Games for its final two sequels — to return for this week's episode. "This is my only window for the next nine months," she says with a weary laugh. "The main cast from Catching Fire were on their grand press tour, so I was able to join them at the world premiere in London, then get on a plane to come to New York for Elementary the next day."

She recently wrapped Season 4 of Game of Thrones, on which she plays royal progeny Margaery Tyrell. "Most people know there's a wedding coming, so I don't think I'm giving too much away," she says. "And what a big day it was — the effort the art department went to for the Joffrey [Jack Gleeson]-Margaery wedding was extraordinary, à la William and Kate. It was off the charts." Her role as the rebel Cressida in the two-part The Hunger Games: Mockingjay is considerably down and dirtier. "It's wonderful to be running around in combat trousers and army boots," Dormer says. "That's quite far from any character I've played in the last few years."

Dormer dove into the Hunger Games and Game of Thrones books as research for those gigs, but she has only dipped her toe into Sir Arthur Conan Doyle's Holmes tales. "My reading list is pretty stacked," she says. "Moriarty was only in two stories — to be perfectly honest, he was a plot device — so I just read those pieces. Posterity weaved him into this grand archenemy in the films and so forth."

She and Doherty were pleasantly surprised when hard-core Holmes fans greeted the reveal of Irene's secret identity with approval. "We were ready for some people not to care for it," says Doherty. "But we were hopeful people would appreciate the twist."

"I've had a similar experience with Game of Thrones," adds Dormer. "I'm amazed at how accepting the purists are, and it really does boost my confidence and enthusiasm."

Who will emerge with the upper hand when Holmes and Moriarty tangle again? Dormer remains mum. "They're almost on a level playing field," she says. "In soccer terms, they're 1-all. It's fun to play, because they've both screwed — and I use that word advisedly — each other once. It's tit for tat."

Elementary airs Thursdays at 10/9c on CBS.

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