In 1991, years prior to the events of NCIS, Leroy Jethro Gibbs starts his career as a newly minted special agent at the fledgling NCIS Camp Pendleton office, where he forges his place on a gritty, ragtag team led by NCIS legend Mike Franks.

In early 90s Boston, an African-American District Attorney comes in from Brooklyn advocating change and forms an unlikely alliance with a corrupt yet venerated FBI veteran invested in maintaining the status quo. Together they take on a family of armored car robbers from Charlestown in a case that grows to encompass and eventually upend Boston’s city-wide criminal justice system.