“NCIS: Los Angeles” is gearing up for a big finale for Season 10. After the introduction of David James Elliott as Harmon Rabb Jr., another big character from the “JAG” TV series will be joining the show in episode 24. The plot will continue to focus on a group of ISIS sympathizers who are planning an attack on a U.S. target.

Callen (Chris O’Donnell) and Sam (LL Cool J) will be on the USS Allegiance, helping Harmon to uncover an ISIS sympathizer onboard the ship. The two were there on the aircraft carrier in the previous episode, but they could not locate the terrorist in time.

Although it has been confirmed that the ISIS sympathizer is there on the USS Allegiance, a preview video of the next episode teases that the aircraft carrier itself may not be the target of a terrorist attack.

Harmon and his team will get some additional help, thanks to Hetty Lange (Linda Hunt). While Callen and Sam search for the terrorist on the aircraft carrier, Hetty will enlist the help of her friend Navy Lieutenant Colonel Sarah “Mac” Mackenzie (Catherine Bell).

Callen and Sam already know that the terrorists are using the chat function in a video game to communicate. A scene from the previous episode confirmed that someone on the USS Allegiance played the game “Viking War Blood” and communicated with other terrorists to plan an attack.

The terrorist strike appears to be sanctioned by the Russians. According to the promo pictures of the next episode, Hetty and Sarah will meet with a Russian diplomat to get the information they need about the terrorist strike.

The promo pictures also tease Kensi (Daniela Ruah) and Deeks (Eric Christian Olsen) meeting with a group of terrorists in what appears to be the middle east or Africa.

“NCIS: Los Angeles” Season 10, episode 24 is titled “False Flag.” The episode will air on May 19 at 9 p.m. EST on CBS Television Network.

Sam and Callen search for ISIS sympathizers in "NCIS: Los Angeles" Season 10 finale episode.