The body of a Marine leads Gibbs and McGee to the NCIS OSP division in Los Angeles, where a murder investigation quickly climbs to a matter of national security in which the two offices must work together to resolve. Meanwhile, Tony begins to snoop into Ziva's personal life.

With the appearance of Mossad agent Michael Rivkin, Tony is forced to question Ziva’s loyalty to NCIS. Meanwhile, in Los Angeles, Special Agent Callen goes undercover to try to catch a terrorist cell while OSP psychologist Nate Getz discovers the startling truth about Gibbs and Special Agent Lara Macy’s relationship.

NCIS agents from Washington, D.C., Los Angeles and Hawai’i, all in D.C. to attend the retirement party of a beloved Federal Law Enforcement Training Center (FLETC) professor, find themselves jointly investigating his shocking suicide.

The crossover continues on NCIS: Hawai'i S02E10 Deep Fake (II) and NCIS: Los Angeles S14E10 A Long Time Coming (III).