Katharine McPhee Katharine McPhee

Nick Jonas may be popping in tonight to play a former theater kid-turned-sitcom star, but it's Katharine McPhee's Karen who grows up — and grows a spine — when rehearsals for Marilyn: The Musical finally get under way. "We'll see her step into her own," says the triple-threat stunner, whose character gets a much-needed lesson in working what she's got, courtesy of some helpful fellow chorus members and a kick-ass Adele tune.

McPhee's own evolution has been equally applause-worthy, as she has gone from Idol runner-up to struggling pop star to an acting breakout. Fitting, since that was her plan from the get-go.

"Long before I went on American Idol, I was passionate about acting and knew that's what I wanted to do," she says. "Music was just something I fell into." It's a good thing, though, as it was her stint on Idol that caught the eye (and ears) of Smash executive producer Steven Spielberg.

"When I heard about this show, I was like, 'What doors do I have to bust down to get this?!'" says McPhee. So watch your back, Ivy Lynn. If this girl can break down doors, you just know she can bring down the house, too!

Smash airs Mondays at 10/9c on NBC.

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