Matt Bomer and Treat Williams Matt Bomer and Treat Williams

"If I told you, I'd have to kill you."

For an actor who's best known for playing warm and heroic characters such as Everwood's Dr. Andy Brown, Treat Williams sure has the act — and dialogue — of a mysterious man on the run down pat — and with good reason.

On Tuesday's new episode of White Collar (9/8c on USA), Williams begins a six-episode arc as Sam, the former partner of Neal's close friend, Ellen (Judith Ivey). Just as Neal (Matt Bomer) was beginning to ask Ellen more questions about his corrupt cop father, Ellen was killed and her last piece of advice to Neal was to find Sam. After weeks of searching, Sam will finally show his face to help solve her murder.

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"The most important thing is that he's driven by finding out who killed his partner," Williams tells "That's why he comes to New York. It's why he's dealing with the FBI. It's why he's dealing with Neal."

Considering Sam's ties to Ellen during her time on the force — the same way she knows Neal's dad — Sam may also know some very valuable information about Neal's pop. But Neal will have to work for it. "[Sam]'s on the run for his own reasons and consequently, he trusts no one," Williams says. "There's a lot of testing of one another before Sam is going to give Neal any information because the guy is working with the FBI and Sam has had his own issues in the past. He has to be very, very cautious."

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Sam will have an even harder time warming up to Neal's partner in crime-solving, Peter (Tim DeKay). "Obviously, the last guy Sam wants to deal with if he's on the run is the guy from the FBI, so his mistrust of Peter is greater than of Neal," Williams says. Those emotions in front of the camera were in stark contrast to the sentiment behind the scenes since Williams and DeKay had worked together before. "Tim's character (the town reverend) was very, very important on the first season of Everwood so it was like coming home," Williams says.

Williams also fit in thanks to his many years logged on Broadway musicals such as Hair and Grease. The White Collar cast is known for breaking out into "song bombs" between takes, and Williams was happy to join the chorus. "Are you kidding me? I'm the worst," Williams says, citing his favorite artists like Frank Sinatra and Tony Bennett. "I tend to croon the oldies."

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In addition to performing the classics, Williams also saw the role of Sam as a throwback to some of his earliest roles. "It's come full circle. I hadn't played a hardened veteran. I was always the young cop back in the day," he says. "It's just wonderful to now play an ex-cop whose life has not been easy. There's a kind of gravitas I can give to this that I couldn't give to those characters 30 years ago."

Although the role of Sam has been clouded in mystery, the less Williams knew, he says, the better. "Script to script, I kept saying I don't really want to know where we're going with this," he says. "At first, I was an actor that needed to know everything: before, after and middle. But after the two scripts, I was so impressed with Jeff Eastin and Jeff King's control that I said I don't need to control this. I've done some work on television where I've needed to work on the script a great deal."

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It's this quality of writing on the small screen, Williams says, that has pulled him towards the medium frequently as of late, in guest stints on Law & Order: SVU and Leverage. After years of headlining series like Everwood and Heartland, Williams has enjoyed jumping from set to set. "It was a little weird at first because I was used to having my own space and feeling comfortable, but I've learned how to do this," he says. "It's a lot of fun to come in and try to find a way to be a part of the show.  I think I've learned how to find my way in more quickly than I would have when I was younger.

"I am a gun for hire," he added.

Watch Neal come face-to-face with Sam for the first time in this exclusive clip from Tuesday's episode:

White Collar airs Tuesdays at 9/8c on USA.