By Peter Bowes
BBC News, Los Angeles
The show's main characters were introduced in a pair of crossover episodes during the last season of NCIS
Yet another spin-off has hit UK TV screens.
NCIS: Los Angeles is based on the original NCIS, a series which has proved hugely successful around the globe.
In the television world, the spin-off game can be risky. The TV landscape is littered with cop shows, legal dramas and medical series. Friends was a sitcom giant, but Joey failed to captivate audiences. CSI: Crime Scene Investigation spawned two spin-offs - New York and Miami - and both have been rating successes.
NCIS: Los Angeles features the special agents of the Naval Criminal Investigative Service working undercover. Chris O'Donnell and LL Cool J play the lead characters.
"It's obviously a spin-off of the original show, NCIS," explains O'Donnell, who played Robin opposite George Clooney and Val Kilmer in the 1990s Batman movies.
"Our show is based on the Office of Special Projects in Los Angeles. It is a new cast of characters, but there is some overlap," he says.
The main characters on NCIS: Los Angeles were introduced in two crossover episodes during the last season of NCIS. The plan is to continue merging the two shows, although the Los Angeles series will remain a separate entity.
O'Donnell says he's aware of the risks in trying to emulate an already successful show.
"We've had the good fortune of having a terrific lead-in with the original show, and being a spin-off and getting to do two episodes of their show last year to introduce our cast was a great benefit, but it's a tough business.
"We've all been on shows that didn't make it - we've all had successes and failures and that's just part of the business."
"You don't need to be familiar with the original show to understand our show or be a fan of our show," adds LL Cool J.
"You can definitely go in with cold feet and - at the same time we want to make sure that we're respectful of those original fans, and hopefully maintain the elements that made the original show successful," he says.
"We're maintaining the same wit, the same humour, the same banter as the original, but the undercover aspect gives us a bit of flexibility," adds LL Cool J.
"We don't have to be in a suit and tie every day - we get to wear different things and assume different roles within the world of special projects."
As television's new double act, the actors appear to have developed an engaging on-screen chemistry.
"We've just hit it off really well," says O'Donnell.
"The audiences fall in love with characters and that's what we're trying to do - develop characters that people can relate to and have fun with, and want to tune to in every week."
The drama is filmed on location throughout Los Angeles. In fact, the urban sprawl becomes a character in its own right.
"LA is one of the great cities in the world," says O'Donnell.
"People want to see it, they want to know what's going on. It's an exciting, sexy city.
The city of Los Angeles becomes a character in its own right
But the actor, who has five children, says he had personal reasons for accepting a role in an LA-based show.
"For selfish reasons I really wanted to be in one city - so that my kids didn't have to lead the gypsy lifestyle that I've lived for so much of my career," says O'Donnell.
LL Cool J has long since made the transition from rapper to actor, having appeared in a number of TV shows and movies, under his real name, James Todd Smith.
But a lead role on a successful primetime drama is one of the entertainer's highest profile jobs.
"This is for me the most exciting and the most special thing that I've been involved with since my music launch, and since my life in that particular niche and genre exploded and did well," he says.
"This is something that is worldwide, that is mainstream and new. I'm being introduced to people who have never heard of me.
"This is not about rapper-turned-actor, this is not a hobby and I'm not moonlighting. I'm an actor on a show and I'm excited about it."