Chris O'Donnell and LL Cool J

“Mark Harmon told me, ‘Your wife is going to hate you this time next year,” says Chris O’Donnell, who costars with LL Cool J (real name: James Todd Smith) in NCIS: Los Angeles, the first spin-off of CBS’ wildly popular NCIS series headlined by Harmon. The stars—who call themselves “9 by 2” for having nine children and two wives between them—thought a TV schedule might provide them more time with their families, but several episodes into production O’Donnell is beginning to understand Harmon’s warning. “I feel like I’m married to Todd all of a sudden.”

Their professional marriage is definitely in the honeymoon stage, despite disparate backgrounds (O’Donnell’s a Chicagoan; LL Cool J is from Queens, NY). “I like to needle people, get in people’s faces a little bit off camera,” says O’Donnell of breaking the ice with his costar. “That’s how I get to know people. And as big a star and well-known iconic figure in his world as LL Cool J is, he’s just been one of the guys.” LL Cool J seconds the sentiment, “Chris and I immediately hit it off. We were able to connect on a sincere level without changing who we are.”

The show—which extends the brand of the naval-crime procedural to LA—is taking advantage of shooting at home, with sequences filmed everywhere from Venice and Malibu to Koreatown and Echo Park. “LA is serving as a phenomenal character,” says LL Cool J. “It’s really a cast member to a certain extent.” O’Donnell agrees, “[LA] is one of the most exciting cities in the world, and they really want to take advantage of that. You can see in the first few episodes they are stamping it as ‘We’re in Los Angeles.’”

The expectation for big ratings is high and the buzz is palpable—so much so that a recent night shoot on Hollywood Boulevard required several retakes because buses plastered with ads for the show bearing the stars’ faces kept driving by in the background. “We had to edit that out,” says LL Cool J. “But that was a cool thing!”