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.

Monica becomes the target of an unknown shooter in Hollywood; Deeks, in an undercover role as Max (at the direction of Granger), rescues her; Monica is a hostess at a nightclub, which is a property of a South African who's now a legitimate businessman, but who previously worked as an international dealer in illegal arms. G and Sam visit the club, and Nell identifies the shooter as Pieter, an enforcer from South Africa; G and Sam take a different tack with Pieter, so they meet him and take him to the boathouse; Max has an unusual short-term relationship with Monica, who steals blood diamonds and shows them to Max, then both she and the stones disappear, but Kensi and Deeks find her and them. G and Sam chat with Pieter, who reluctantly talks; Kensi and Deeks chat with Monica, who agrees to cooperate; the team monitor an exchange, minimize the damage, and grab three bad guys; later Kensi and Deeks get something clear. Granger never shows up.

A nuclear bomb explodes in a desert in Mexico; G and company investigate; Sam and Michelle go underground; G and Kensi go to Iran and bring back the Chameleon, who takes part in a complex deal to gain the two missing bombs. [Continued.]

G, Kensi, and the office crew continue to pursue the wrongdoers and the missing nuclear bombs while Sam and Deeks remain in custody; later the team gather on a helipad, where they hold a shootout; a NEST team seizes the bombs.