NCIS: Los Angeles NCIS: Los Angeles

NCIS: Los Angeles loves to blow things up. So when executive producer Shane Brennan received word that the CBS drama would air a two-hour finale, he was practically giddy.

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"There's a particularly amazing explosion in the second hour of the show ... and there are no computer graphics in this explosion," Brennan says. "The debris is real, the fire balls are real. We have this opportunity of doing a double episode and we ended up with a movie in effect. I don't think in 30 years of doing this, I've ever had a more challenging two hours of TV to put together."

But while things may go boom early and often, look for a lot of other explosive moments between the characters, especially Callen (Chris O'Donnell) and his nemesis The Chameleon. When the team is called in to assist the returning Agent Renko (Brian Avers), whose cover may have been blown, Callen & Co. quickly find they have all been playing into The Chameleon's hands.

"The episode's title ['Sans Voir'] is French. It's a term in chess meaning playing blindfolded," Brennan says. "When you're playing chess with someone and you're not in the room with them, you have an advantage you're playing in your head. This is especially true for Callen and the Chameleon."

Unlike past season finales, don't look for a big chunk of Callen's mysterious past to be revealed. However, Brennan teases that there will be some breadcrumbs for fans of that mythology, thanks to Hetty (Linda Hunt).

"The episode forces him to sit down with Hetty and have a conversation, and it's kind of a watershed conversation for both of them," Brennan says. "She pulls the curtain down. There's one little tease in there, but [the episode's] really about Callen facing a very emotional test. Callen is taken right to the edge and tested until he breaks. It's a very unsettling ending."

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How unsettling? Well, CBS' promos have been teasing a shot of Hetty in a morgue with two dead bodies."Nothing is ever quite as it appears, and that's what the show is about," Brennan says. "Hetty is someone who's always working her own particular game. But I've got to say it doesn't end well for a lot of people in this two-hour finale. There are two bodies, and those things, very sadly, are what they seem."NCIS: Los Angeles airs its two-hour Season 3 finale Tuesday at 9/8c.