-A Naval Officer dies after his water is laced with cyanide. NCIS finds that it was a trial run for a larger cyanide killing when they find five barrels of the poison stolen.
- First a neighborhood is targeted. NCIS finds a vacant home was used to spread the cyanide into the water supply. They track the truck to a rental agency and find out the owner was the culprit.
- A protest group Designing a New America (DNA) is suspected in the attacks. Callen attends a rally and punches Sam dressed in his military uniform. This gets Callen invited into the group. His cover is blown when a previous witness is part of the group. He poisons Callen with cyanide, but Callen uses a counteragent to save himself.
- NCIS finds the location for the next attack and prevents the cyanide from being released.