A nuclear bomb goes off in an unpopulated area of Mexican desert, signaling to the NCIS:LA team that arms dealer Isaak Sidorov is eager to sell his two remaining, fully-functional nuclear weapons. Callen and Hetty devise a plan that involves extracting Marcel Janvier, the Chameleon, from Iran and having him broker a fake arms deal with Sidorov. Sam and Michelle go back undercover inside Sidorov's operation with some help from Deeks, who arrests all of Sidorov's bodyguards. Callen gradually gets Janvier to agree to participate in the set-up, which suffers a setback when Sidorov demands that they meet in a place that forces our heroes to keep their distance. At the meet, Janvier manages to pass a message over to Sidorov, unbeknownst to Callen, who is furious when the mission goes sideways, putting his loved ones in danger. Sidorov then arranges for Sam and Michelle to be separated, and he gets the drop on Sam and Deeks, kidnapping them. Meanwhile, Michelle gets attacked by two female Russian assassins, and Kensi rushes to help her before its too late. The season ends as Sidorov begins to torture Sam and Deeks, urging them to admit that they are federal agents.