Don Lambert, a key witness in the case against Hugo Garza, a notorious international arms dealer, is blown up before he can testify at trial. The NCIS team investigates the blast and soon traces the source of the bomb.
Meanwhile, Pride and Percy go to Texas to retrieve the only other possible witness to testify against Garza. Maslow is smug about the situation, using it to humiliate and taunt Pride, but agrees to testify against Garza.
LaSalle and Brody track down the assassin, Ethan Greer, who has a long list of weapons-related charges against him. He is, unfortunately, too dead to provide them with the identity of who hired him, and there are no apparent links between Greer and Garza.
They are, however, able to find a link to Zed Hastings from the militia movement Pride infiltrated in NCIS: New Orleans Season 2 Episode 1. Even as they make the connection, Pride and Percy are ambushed. They are eventually able to gain the upper hand and return to New Orleans.
Maslow testifies against Garza, but someone visits Zed Hastings in the hospital, indicating that Hastings wasn't acting on his own initiative at all and that Pride is still very much in danger.