This episode picks up where episode 405, "Out Of The Past", left off. Sam, Callen, and the rest of NCIS race to track down the remaining sleeper agents with nukes on the list left by ex-CIA agent Frank Turner. According to the list, there are nine Russian sleeper agents in the seven largest US cities, but the joint raids run by NCIS and the FBI turn up no other nuclear bombs. Based on the evidence, it appears that Russian arms dealer Isaak Sidorov has located at least three of the bombs and will attempt to tell them to the highest bidder on the black market. CIA Agent Michael Snyder corners Sam and tells him that they need to plant an agent in Sidorov's inner circle to gain information about the bombs; someone Sidorov has a history with. After much debate, Sam and the team stage an attempted assassination on Sidorov, which tricks him into contacting an old friend for help. That old friend is the undercover agent, a gorgeous woman named Quinn. Sam seems very hesitant about the whole operation, and we later learn that it's because Quinn is actually his wife.