A scientist working on a highly classified DARPA project is killed by a sniper while jet-skiing on the beach. As NCIS investigates, Sam and Callen find his business partner bludgeoned to death in their offices. As the team compares evidence from both crime scenes, Leon Vance arrives, announcing the sniper is Lee Wuan Kai, a highly skilled assassin he’s crossed paths with before; once nearly killing him. Vance is surprised when Lee Wuan Kai calls him and tells him she didn't kill the business partner, she takes pride in her work and doesn't want that messy kill attributed to her. As Kensi, Nate and Dom investigate the death of the business partner, Vance puts pressure on Sam and Callen to not to let Lee Wuan Kai escape justice this time.