Mr. G Callen isn't the only NCIS: Los Angeles agent who knows how to go rouge.

The OSP's former shrink is back for "Head of the Snake", and Nate Getz (Peter Cambor) ready to cause a little trouble.

"After Operational Psychologist Nate Getz (Peter Cambor) fails to check in with Hetty while working undercover on a mission linking organized crime to terrorism, the team learns he is working with an infamous crime leader," CBS teased.

Is Nate really on the wrong side? We sure hope not, but teasers from Entertainment Weekly  seem to indicate otherwise. One thing is for sure - Callen (Chris O'Donnell), Sam (LL Cool J), Deeks (Eric Christian Olsen), and Kensi (Daniela Ruah) will need to bring their 'A' game if they want to figure out what's really going on.

"After going dark for three months while on a long-term undercover op tied to terrorism in L.A., Getz resurfaces on security footage stealing a military transport of weapons," Entertainment Weekly teased. "When Callen and Sam track him down, he double-crosses the duo, taking Callen hostage and torturing him for information."

Nate usually pops up when a member of Hetty's (Linda Hunt) team goes through a traumatic even - e.g. Nell's (Renee Felice Smith) first kill, Deeks and Sam's torture - but episode 21 won't be Cambor's first trip into the field. Hetty's team previously provided backup when Nate worked to suss out a terrorist cell from inside a prison.

Unfortunately, fans will have to wait an extra week for NCIS: LA's rocky reunion. CBS will air a repeat on April 4, which means "Head of the Snake" won't air until April 11. Season 7 is winding down, and only "Head of the Snake," "Granger, O," "Where There's Smoke...," and "Talion" are the only episodes left before the summer hiatus.

Catch NCIS: LA Mondays at 10 p.m. ET on CBS.

Tags: NCIS: LA NCIS: Los Angeles television CBS