The death of an American seaman on a U.S. nuclear submarine during an AUKUS ceremony on Sydney Harbour is investigated in a joint effort between America's NCIS agents afloat and the Australian Federal Police.

When the body of a long-missing U.S. Naval engineer is discovered buried in concrete, the team enlists Doc Roy's old friend to assist in the investigation.

With a Stinger missile and murderer in the wind, and Darwin's World War II Commemoration ceremony fast approaching, NCIS: Sydney races to prevent a deadly attack.