NCIS: LA's 100th Episode: Callen Gets a Blast From the Past

NCIS: Los Angeles celebrates 100 episodes this week, and viewers will get some long-awaited answers about Callen's (Chris O'Donnell) past, according to showrunner Shane Brennan.

"I've been waiting 75 episodes to tell this story," Brennan tells TVGuide.com. "I came up with this way back in Episode 25. I knew what I wanted to do. I had my fingers crossed that we'd get to the 100th episode so I could do it. And along the way, we filled out more and more of Callen's backstory, but each one of those pieces was shaped so that it would fit into this piece of the puzzle here that we reveal in Episode 100. So the audience is going to get a large chunk of backstory here that they will find incredibly rewarding."

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As shown in the clip below, Callen comes face-to-face with a kidnapping victim who claims to be his father. And that's not the only blast from his past. Callen will find himself once again tussling with the Comescus, the Romanian family that killed his mother.

"It's one thing for them to go to Romania ... and for them to poke the hornet's nest over there. It's an entirely different thing to have the hornet's nest land in Callen's lap in Los Angeles," Brennan warns. "This is kind of a showdown. ... It rolls into the room like a live hand grenade."

The fallout from this latest clash may be catastrophic, warns Brennan, especially once Callen and the team realize that he might be the kidnappers' real target. The situation is particularly concerning for Hetty (Linda Hunt).

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"She knows Callen better than Callen knows Callen," Brennan says. "She's very protective of Callen, and doesn't want him involved. In fact, she tries to keep the truth from him about his father to protect him. ... She doesn't want him out there."

But while the episode will provide plenty of answers, Brennan promises: "It is not the end of the Callen story. We have at least another 100 episodes, I would think, to explore more about Callen and who he is and his identity."

Check out a clip from the episode's opening sequence below:

NCIS: LA airs Tuesdays at 9/8c on CBS.

(Full disclosure: TVGuide.com is owned by CBS.)