The investigation begins when a Navy lieutenant is lethally poisoned by cyanide in a communal water jug. The team quickly discovers this was merely a trial run for a much larger attack by a radical protest group known as "Designing a New America" (DNA). Their goal—allocating the defense budget to education—is noble on the surface, but their method is murderous. Standout Moments & Character Dynamics
Critics from TV Fanatic rated the episode a 4.2 / 5.0 , praising the strong team interaction and the focus on core cast members rather than outside guest stars. While some plot points were deemed predictable, the ideological conflict presented by the DNA group added a layer of complexity often missing from standard procedurals. NCIS: Los Angeles Season 4 Episode 20 Recap: Purity
: Kensi Blye (Daniela Ruah) and Marty Deeks (Eric Christian Olsen) provide the legwork, with Deeks notably diving into a dumpster to find a critical syringe.