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 a shark spits out an arm wearing U.S. Navy equipment, the team's investigation tests the loyalty of a band of former Navy divers.

When JD's son is kidnapped by an international assassin in exchange for a wanted criminal in NCIS custody, the team frantically tries to get his son back safely without trading in a criminal.