NCIS: Los Angeles: Season 1, Episode 7

1 - 7: Pushback

The team investigates the murder of the Russian woman who was present when Callen was attacked. While searching through her files they discover a file concerning an operation codenamed "Cossack" that Callen was a part of in Russia. Callen, his partner in the DEA (where he was working then) and a CIA agent were betrayed before they could start their mission. The two other agents were also attacked and killed. Callen believes that their ex-KGB control officer was the traitor and he goes to him to find evidence that he was the traitor. It turned out that he too was attacked but survived and tried to warn the others using the Russian girl, Alina Rostoff, Callen's foster sister when he was 14. It soon turned out that the traitor was the CIA agent who had faked his death so as not to be suspected and who was now the leader of the Russia crime syndicate that was "Cossack"'s target. After arresting him, Callen went to the home where he and Alina had spent three months together as brother and sister.