Standing in the NCIS: LA headquarters, Chris O’Donnell and Gary Cole are all smiles.

But then someone calls out “action!”

and the mood instantly changes.

NCIS

(L-R) Katrina Law, Vanessa Lachey, Wilmer Valderrama, and Chris O’Donnell on the ‘NCIS’ crossover.Sonja Flemming/CBS

She laughs before adding, “I love my job.”

“It’s like all the superheroes of procedurals coming together for the first time in history.

It’s iconic,” Valderrama marvels.

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Gary Cole, Vanessa Lachey, Sean Murray, Wilmer Valderrama, Noah Mills, Katrina Law, and Brian Dietzen on the ‘NCIS’ crossover.Sonja Flemming/CBS

“It felt like we’ve been doing that for years together, not as separate groups.

That’s pretty special,” he says.

“There’ll be action.

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Vanessa Lachey, Jason Antoon, Tori Anderson, and Gary Cole on the ‘NCIS’ crossover.Karen Neal/CBS

There’ll be thrills.

There’ll be rollercoaster rides.

“It logistically is really challenging for the production.

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Alex Tarrant and Chris O’Donnell on the ‘NCIS’ crossover.Karen Neal/CBS

And it’s tough on the writers,” O’Donnell says.

That’s really a challenge.

All the credit goes to the writers and the producers that are able to make it work.”

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Wilmer Valderrama and Vanessa Lachey on the ‘NCIS’ crossover.Michael Yarish/CBS

And there’s a really important NCIS member who’s missing as well, so it gets crazy."

O’Donnell loves how the threat level is more intense than ever.

We’ve got to watch our step here.

“All three shows have their own distinctive styles,” Cole explains.

We’re all just carrying our little pistols around.

And Hawai’i has great weather.

The challenge is to get comfortable as quickly as you’re able to.

Valderrama was especially excited to see how each show’s tone was brought together into one story.

“TheNCIS-verse, the fans always wanted it,” LL Cool J says.

So this was a natural step and a natural progression to me.

It’s fun, it’s innovative.

And now they’re piercing a veil and crossing into another world.

They’re getting to see how these characters interact and the energy around it is special.

It feels like it’s the beginning of something beautiful."

Cole is “sure” that fans will see more three-show crossovers in the future.

“I think that makes sense.