NCIS: Los Angeles is getting a blast from the past, and two agents are about discover there is a lot more to their first-ever case then they realized.

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It may be the season of Deeks (Eric Christian Olsen) and Kensi (Daniela Ruah), but NCIS: LA will be thrusting Callen (Chris O'Donnell) and Sam (LL Cool J) back into the spotlight for "Tuhon."

Tuhon (Danny Trejo), an assassin linked to the partners' very first case, will be back on their list of suspects following the death of a diplomat. When Sam and Callen head south of the boarder to investigate, they realize Tuhon has connections to someone inside NCIS.

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"We don't flash back and see them [during their first case], but we discover how they first met. It involved a character called Tuhon, played by Danny Trejo, and an unresolved case," explained series creator Shane Brennan, according to TV Line. "Here we are, six years later, and Tuhon's back in circulation, back on their radar, and we discover a whole lot more about that character than they ever knew when they first went after him. What we learn is that he has a very close connection to Hetty."

While Hetty (Linda Hunt) may not look it, she is easily the most terrifying member of the Office of Special Projects. Aside from her weapons mastery and her layers of mystery, however, the formidable leader does have a very caring center.

"I think [Tuhon] could well have a soft spot for Hetty.... Hetty has a soft spot for everyone, but she can also just cut 'em off if she needs to," Brennan told TV Line. "It's a great episode with some amazing action sequences in it, and yet at the same time you're taking this tough, scary guy and showing the other side of him. And for Sam and Callen, it's much as a surprise for them to see what he's really like."

"Tuhon" will air on Feb. 25 at 9 p.m. ET on CBS. Click here to see photos from the episode, and check out the video below to see a preview for NCIS: LA's most recent episode, "War Cries."