If Nucky Thompson (Steve Buscemi) is the heart and soul of "Boardwalk Empire," Michael Shannon may just be its conscience.

At the very least, Shannon's Agent Nelson Van Alden is one seriously painful thorn in Nucky's paw.

"Certainly, one of the themes of the show is 'Can virtue survive in Atlantic City, or does it corrupt everything, everyone that steps across its borders?'" Shannon, 36, said. "It's a real David vs. Goliath situation. For Christ's sake, they're office is a post office. There's not a huge force of people working on this."

Of course, this being "Boardwalk Empire," the virtuous lawman isn't without his dark places. One look at the scene in episode three where he tries to get an injured man to talk by shoving his fist into an open wound and you know Van Alden's white hat isn't without its smudges.

For Shannon, an Oscar nominee for the 2008 drama "Revolutionary Road," that duality made committing to the rigors of series of television - even on a series as relatively flexible as the ensemble-driven "Empire" - a no-brainer.

"You know, I like to roam and do different projects and work with different people. I was certainly hesitant for a long time to approach being a regular on television," the actor said. "But there are some qualities that are different with working with HBO. I actually wound up enjoying it a tremendous amount, even moreso than I thought."

Series creator Terence Winter first saw Shannon years ago at the Barrow Street Theater in Manhattan. The actor was starring in a play titled "Bug," and Winter was struck by his intensity.

When casting director Ellen Lewis suggested Shannon as Van Alden, Winter was sold.

"He brings a level of intelligence, dedication and intensity to his character that was more than I could have hoped for," Winter wrote in an e-mail.

Already, we've seen a few different shadings from Van Alden. There is the dogged pursuit of justice, yes, that borders on obsession. But also a sterile, stunted home life, and a fascination with Margaret Schroeder, played by Kelly Macdonald. It's almost as if he and Nucky will engage in a tug-of-war for her soul.

"First of all, I think she's very vulnerable," Shannon said. "I think Van Alden, in an ideal world would be, to himself and other people, a kind of angel, and nothing would make him happier than to be the person that protects Margaret from all the corruption and evil in the city."

Tonight brings the series' fifth episode. Winter suggests you stick around, because Shannon's portrayal really heats up later in the season. It's a sentiment the actor shares; he won't give any details, but suggests any twists you didn't see coming with Van Alden in the first half of "Boardwalk Empire's" first season will be trumped in the final few episodes.

"When you shoot the pilot, you don't know what's happening in episode 12. You get each script and the character is unfolding in front of you. It's a very neat challenge," Shannon said. "It doesn't feel very confining."

Contact Kevin Clapp:

609-272-7255; KClapp@pressofac.com

'Boardwalk Empire'

Airs 9 tonight on HBO