Season four of NCIS: Los Angeles begins where the third season ended with Callen facing the fallout of shooting The Chameleon. He is forced to continue investigating alone and is kidnapped after by Iranian hit men. The team tackles many exciting and difficult cases including investigating the death of a former Marine killed in a drone strike on a terrorist target in the Middle East. Later, Nell goes undercover in an experimental strategy game developed by the Office of Naval Intelligence when four participants are killed in a restaurant bombing. In a two part episode, Sam receives a prerecorded phone call from a former coworker and ex-CIA agent asking for his help after he is murdered. The team is eventually led to Soviet sleeper agents in possession of a nuclear bomb, and races to find them before it's too late.