A Navy captain dies of gunfire while with his fiancée, who is Gibbs's first mother-in-law. While Gibbs and company investigate, they find several discrepancies and inconsistencies. Gibbs figures it out, and he and "MAllison" work it out.

The body of a Navy petty officer, shot and drowned, washes up on a beach; while Gibbs and company investigate, another body, wrapped in chain, turns up. The FBI becomes involved, the gang find clues, and Fornell and Gibbs find a leak.

A Navy captain dies by gunfire; Gibbs and company investigate; the gang meet Emma, a pregnant Marine first lieutenant, who says that she's the real target. The team figure out the pieces, and they deal with the problems and the bad guys.

Gibbs and the gang continue to pursue Dearing, the explosions, and the disappearance of the director; Dearing continues to mess with Gibbs and Ryan. After another explosion and another death, disaster strikes at the Navy Yard. [Continued.]

Within 30 miles of Washington, DC, eight kids in Navy and Marine Corps families have suddenly become badly ill, requiring treatment in ERs and ICUs; Gibbs and company investigate; Carol, of the Naval Medical-research Center, joins the effort; immediately the number of sick kids grows to 14, then 19, 23, 28, and 34, and none of them responds to treatment. Duckie announces the first fatality, who was a veteran of Vietnam, then he describes the cause of death and the treatability in the kids. Abby says that she has misidentified the particular nature of the illness, so she, Jimmy, and Carol keep working, and they eventually nail it. Abby gives Jimmy a lecture about kindness, optimism, and parenthood. Then the gang identify an international traveler who in many places has recently encountered many kids and the fatality. Meanwhile Vance has three tense chats with his estranged father-in-law and then a nicer one.

A distracted texting driver runs over the dead body of a Naval officer; Gibbs and company investigate; they find a connection to a previously unreported rape of a drugged victim. The team figure out everything, and they catch the bad guy.

When an openly-gay Navy Lieutenant who was about to be awarded the Medal of Honor is murdered, Gibbs and the team investigate. Meanwhile, Breena goes into labor.

Investigating the death of an intruder at Quantico, Jimmy and Kasie are exposed to a deadly bio-toxin. The NCIS team calls on Doctor Carol Wilson for help as they race to find the antidote. Torres tries to distract Jimmy's daughter, who came to spend the day with her dad.