At a federal building in downtown Los Angeles, California, a lone woman, armed with a shotgun, seizes a Navy recruiting station and takes all hands as hostages; G recognizes her as Tracy, his former partner, using an alias, which they used while undercover for the CIA; G, Sam, Kensi, Nell, and Deeks all speed to the site. With the consent of the LAPD cop in charge, G goes inside the building and talks with Tracy, who concedes that her purpose is to get in touch with him; she says that she's undercover for someone in the private sector, that a white-supremacist group has chased her, and that she needs his help. Kensi and Deeks go elsewhere and find the body of an agent of the FBI. Tracy discloses more, G makes a plan, and, following it, they escape to the boathouse, where they meet Sam; Tracy reveals more, then the team make another plan and pursue it; eventually they grab the illicit arms dealer behind the whole thing, then they learn the rest of the story.
—DocRushing