Julie Chen is trying on her acting shoes.

The Talk co-host guest-stars on Monday's episode of NCIS: Los Angeles as Nancy Kelly, a U.S. Ambassador to Tunisia who narrowly escapes an assassination attempt. Sam (LL Cool J) and Callen (Chris O'Donnell) are brought in to get to the bottom of the terrorism plot, and the episode contains "the shootout of all shootouts" as a result. Check out a sneak peek below.

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This is the first time Chen is portraying a fictional character instead of appearing as herself (as she's done on Madam Secretary and The Millers). Earlier this week, the Big Brother host - who says she rehearsed her lines "15 to 20 times" with her husband, CBS president Les Moonves - tweeted a behind-the-scenes picture of herself on the NCIS: LA set.

"This has been very intimidating to me," Chen says in the sneak peek, exclusive to TVGuide.com. "I'm not a trained actor. I don't remember feeling this scared since I first started my career and I had to give my first live report. ... It's a new venture for me."

NCIS: LA airs Mondays at 10/9c on CBS. Check out a sneak peek of Monday's episode below.

(Full disclosure: TVGuide.com is owned by CBS.)