'NCIS: LA' Boss on 'Ambitious' Finale: It 'Will Move You to Tears' (Exclusive Photo and Video)

When you have two hours to close out an eventful season, it's a tall order. As NCIS: LA boss Shane Brennan previews, tonight's big two-parter will leave everyone on the team hanging. (Plus, an exclusive photo and scene from the NCIS: LA finale.)

Brennan, who wrote Part 2 of the two-hour closer, likened the episode to a very ambitious movie.

"It's probably the most ambitious two hours of television I've made in 30 years of doing this," he told The Hollywood Reporter. "Both of them are very big episodes, the second one in particular is a very big episode certainly from a production point of view, but creating the story that cranks up and doesn't let you go."

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The finale sees the NCIS: LA team going up against one of its toughest criminal: The Chameleon. The culprit lures Callen (Chris O'Donnell) and the crew into a mind game that affects everyone's state of being. In an exclusive scene to THR above, team members Kensi (Daniela Ruah) and Deeks (Eric Christian Olsen) continue their dysfunctional partnership at the gun range.

"People may want to turn over at 10 o'clock but they won't be able to do it," Brennan says. "The end of the first hour of the finale is just so unexpected. It is so brazen. You have to come back to the other side of the commercial break to see what happens. By that point, we put the audience into the hands of a little lady called Linda Hunt."

The NCIS: LA boss called Hunt "astonishing" during the two-hour finale, teasing that "if you're a fan of Hetty, if you like Linda Hunt, you have to watch the finale -- in particular the second hour." (Brennan revealed that viewers will see Hetty in a morgue during the episode.) Her performance "will move you to tears." Brennan noted that they will be submitting Hunt for Emmy consideration "on the strength of this performance."

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Without going into too much detail, Brennan says that the finale puts Hetty front and center, but it's very much about the way Callen and Hetty react to what's unfolding around them.

Brennan praised the ensemble, calling O'Donnell, Hunt, LL Cool J and company one of the best he's ever worked with. "This group of people gels like no other I've worked with. The chemistry you see onscreen is the chemistry they have offscreen," he says.

Since the series debuted, there have been cast tweaks here and there. Brennan says, "[The audience] should go into the season finale feeling very uncomfortable. .. The outcomes are surprising."

Check out the exclusive photo to THR of the NCIS: LA cast in a rather good mood below: