Last night at a parking garage in Los Angeles, California, at least three gunmen stalk and attack an unidentified woman, who has disappeared; two bad guys and a bystander have died; Hetty cryptically assigns Callen and company to investigate. The fearless foursome find no identifying data about the people involved, but at the boathouse Hetty finds the missing woman, Grace Stevens, whom she knows, and who's a special agent of the NCIS on an undercover assignment; G and Sam arrive, meet her, and learn about her. Kensi and Deeks disguise as a newlywed couple, and Nell does so as a maid; Kensi rescues Nell from a tight spot. G engages Hetty in an intense personal conversation. Grace and the G team set up a sting, pull it off, and suck in the head man and two of his goons. Afterward G again chats with Hetty, who reveals more about Grace's background and her own history and activities.