While Callen suspects Hetty of keeping secrets about his past and Joelle surfaces in her quest to capture Katya, NCIS must track down an informant whose life is in danger. Also, Kensi and Deeks work to expand their family.
Sam and Kilbride clash when a case involving an arms dealer responsible for the slaughter of ATF agents leads them to a well-connected colonel and friend of Kilbride, accused of supplying militia groups with guns. Also, Kensi and Fatima go undercover at a rehab facility to question the arms dealer's girlfriend.
As Callen continues hunting Katya, Kilbride enlists NCIS to help find a truckload of stolen guns. The assignment becomes more challenging when their suspect, the son of a mob boss they believe was planning to sell them, is found dead.
When an NCIS mission to protect a compromised undercover agent goes completely sideways, the agents are individually interrogated to find out what really happened. Also, Kilbride must make a difficult decision.