The third season of NCIS: Los Angeles an American police procedural drama television series, originally aired on CBS from September 20, 2011 to May 15, 2012.

[1] The Special Projects team travels to Romania to search for Hetty, while delving into the history of the Comescu crime family, and their connection to Callen.

The NCIS team has to join forces with the NSA to find the creator and controller of a software program linked to a cyber attack against the Department of Defense.

After a former Navy intelligence officer is murdered, Hetty contacts a former co-worker when the NCIS team uncovers a threat to a pipeline in Afghanistan.

During the middle of the holidays and the distractions they cause, the team is tasked with finding the thieves who stole an experimental electronic device with enough power to destroy half of Los Angeles.

The team investigates the murder of two businessmen and later finds out that a spy/agent named Chameleon who can take on any personality or facade he likes is responsible for the killings.

Later, under pressure from both Hetty and Callen, Granger finally tells them the reason for him coming to Los Angeles: he's here to catch a killer and the camera then shows him looking over at Kensi, suggesting it might have something to do with her.

However as Callen and the team investigate to try and clear their friend's name, they uncover Granger's ties to the unit and begin to suspect that he is the true killer.

Callen & co discover that Granger fled the scene, and they must find him and get answers whilst Kensi continues the chase for the killer responsible for her father's death as she resolves to solve the case once and for all.

When a former Marine is suspected of creating a chemical bomb found in a vehicle, Nate Getz returns to Los Angeles and the team must work together with the FBI to track down and stop a domestic terrorist.

Detectives Danny Williams (Scott Caan) and Chin Ho Kelly (Daniel Dae Kim) of the Hawaii Five-0 task force arrive in Los Angeles to help Callen, Sam and the Office of Special Projects find and stop Jarrod Prodeman (Rob Benedict), a disgraced doctor carrying several vials of smallpox, capable of wiping out half the world's population.

Guest starring: Rob Benedict, Laura Regan, Cynthia Addai-Robinson, Helen Eigenberg, Celia Finkelstein Deeks and Kensi go undercover as a married couple to catch a Russian sleeper agent in the neighborhood.

[26][27] Chris O'Donnell and LL Cool J appeared as G. Callen and Sam Hanna in the twenty-first episode of the Hawaii Five-0 second season titled "Pa Make Loa" ("Touch of Death") on April 30, 2012.