A woman rear ends a truck and discovers a bomb in the back. The FBI takes over the case and arrests a former Marine. Granger wants NCIS to get involved and investigate to see if there is a bigger threat. FBI Agent Ambrose blocks NCIS at every turn. Former NCIS boathouse crew member, Nate, returns to do a psychological profile of the bomber.

A group claims responsibility for the bombing even though the FBI has arrested the Marine. Callen and G track down the Marine's girlfriend and start to unravel the mystery from there.

The Marine is set up for the bombings. His girlfriend unwittingly is sent to meet with FBI Agent Ambrose with a bomb. NCIS gets there in time to save him.