In 1991, years before the events of NCIS, a young Leroy Jethro Gibbs begins his career as a newly minted special agent with the Naval Investigative Service. Operating out of the fledgling Camp Pendleton office, Gibbs works to find his place on a gritty, ragtag team led by NCIS legend Mike Franks as he takes his first steps in the job that will define him.