A TV reporter accompanies a group of ATF agents on a raid of suspected gunrunners; on the deck they find the bodies of five civilian men, already dead, two of whom (career criminals) wear authentic uniforms of the US Marine Corps and bear counterfeit ID cards; Director Vance orders the Callen team to investigate. G and Sam find dead birds and squirrels; Eric and Kensi find telephone traces and a street address, which allow the team to meet Esther, a sweet elderly retired researcher in biological warfare, who now suffers from Alzheimer's disease. Esther tells about her recent work, believing that she serves her country; she tells also about her two "Marine" drivers, who take her to and from a lab, where she recently isolated a protein responsible for botulism. The team find someone who provides answers; Sam goes undercover and attends a party and breaks it up; G musters a number of helpers, who catch the bad guys; G and Kensi go shopping; G and Sam take matters in hand.

Callen and Sam work to locate a group of ISIS sympathizers aboard the USS Allegiance; Hetty enlists her friend to help obtain information from a Russian diplomat.