Callen and Sam will take center stage when NCIS: Los Angeles heads south of the boarder in "Tuhon."

Focus will momentarily shift from the Deeks (Eric Christian Olsen) and Kensi (Daniela Ruah) narrative as Callen (Chris O'Donnell) and Sam (LL Cool J) take a trip down to Mexico following the death of a diplomat. The partners will reunite with a face from their past when an assassin named Tuhon (Danny Trejo) becomes a suspect in their investigation.

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A piece from their very first case together, Tuhon will help to kick off a revealing episode for Sam and Callen.

"It's a big episode that takes everyone down to Mexico, where there's a lot of action as well as character stuff for Callen, Sam and Hetty," said series creator Shane Brennan, according to TV Line.

Meanwhile, back in Los Angeles, Peter Cambor's Nate Getz will also be making a reappearance. The operational psychologist will visit the Office of Special Projects team for the second time this season, and this time he will be wielding a gun.

"Big thanks to @petercambor for another stellar performance. Until next...#NCISLA #bestcastever #bestcrewinhollywood," tweeted executive producer John Peter Kousakis while Olsen posted a photo of Deeks and Nate with their weapons drawn.

In addition, Cambor tweeted a picture of a new business card that lists Nate's occupation as Special Assistant to the Undersecretary of Foreign Affairs State Department. Could the good doctor be returning to Los Angeles for good?

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Set to air on Feb. 18, fans can get a glimpse of the David Kalstein penned episode in the photos above. Click the video below to see a preview of 'Tuhon."

NCIS: LA airs Tuesdays at 9 p.m. ET on CBS.