After the decryption of a list of names, NCIS agents continue the search for both Sidorov, a Russian illegal-arms dealer, and leftover Russian sleeper agents with access to surreptitious nuclear bombs; NCIS teams execute concurrent arrests in seven cities around the USA; however, all seven teams find their targets already dead. G and Sam confer with Arkady; afterward G and Sam meet a tail, which consists of three CIA agents, one of whom, Snyder, Sam knows and dislikes; Kensi, Deeks, and others uncover an empty but radioactive secret room; Eric and Nell find Sidorov; Granger gives an order, but Sam pursues another idea, and Granger catches the team, yet he goes their way; the team watch Sidorov; Sam goes undercover, then he and his wife meet with Sidorov; Snyder allows Sidorov to leave the country (without bombs), but he expects him to return; Sam and Snyder walk into the surf at Santa Monica Bay, where the two of them discuss a disagreement.

One Russian kills another in the LA area; G and Sam quiz Arkady; Sam and Michelle go back undercover for the CIA; Sam lands in jail, and Hetty leaves him there; Greshnev dies, and Sidorov disappears; Hetty says that this is far from over.