“NCIS: Los Angeles” Season 10, episode 23 is huge because there is a major crossover with “JAG” TV series. The promo videos of the next episode tease David James Elliot reprising his role as Harmon Rabb Jr., also known as “Harm.”

A promo video of the next episode shows Callan (Chris O’Donnel) and Sam (LL Cool J) onboard a U.S. aircraft carrier. They will go there to solve a terrorist-related case, and they will need Captain Harmon to solve it.

Captain Harmon has a big entry scene when he meets Callan and Sam. He appears to be piloting an F/A-18 Super Hornet fighter jet in the promo video.

While the return of Captain Harmon will be exciting for “JAG” fans, what will also be equally exciting is the plot of the next episode. Callen and Sam will work together to crack a case related to ISIS sympathizers who plan to target U.S. military locations. The next episode will also build up the finale of Season 10, which airs next weekend.

Callen will take a few days off to get his mind off the incidents in the previous episode. However, a sneak peek scene of “NCIS: Los Angeles” Season 10, episode 23 shows him becoming restless and taking on a case to keep himself busy. All the other team members will be busy with their own work, which will leave Callen to do the investigation with Eric Beale.

The case that Callen will investigate, which will presumably lead him to the ISIS sympathizers, will be about a badly burned body of a former U.S. marine. While Callen will be kind hearted enough to let Eric tag along, he will not be getting a gun while investigating the case.

Sam will get to join Callen at some point during the investigation. Preview pictures of the next shows the two of them investigating a burned down building.

“NCIS: Los Angeles” Season 10, episode 23 is titled “The Guardian.” The episode will air on May 12 at 9 p.m. EDT on CBS Television Network.

"NCIS: Los Angeles" Season 10, episode 23 will be a big "JAG" crossover.