History is the 15th episode of NCIS: Los Angeles Season 4 as well as the 87th episode of the entire NCIS: Los Angeles series.
OSP investigate the death of a former member of a domestic terrorist group, the Gun Barrel Party, a group that in the 1970s was wanted for carrying out a string of bombings as well as domestic terrorism with the investigation growing intense when it's discovered that a supposedly dead member of the Gun Barrel Party may in fact still be alive and living under an alias in downtown Los Angeles.
|G. Callen||Chris O'Donnell||NCIS Special Agent and the leader of the Office of Special Projects field team.|
|Kensi Blye||Daniela Ruah||NCIS Special Agent with the Office of Special Projects.|
|Marty Deeks||Eric Christian Olsen||A Detective with the Los Angeles Police Department and also the LAPD/NCIS liaison.|
|Eric Beale||Barrett Foa||Tech Operator with the Office of Special Projects.|
|Nell Jones||Renée Felice Smith||Tech Analyst for the Office of Special Projects.|
|Henrietta Lange||Linda Hunt||Operations Manager with the Office of Special Projects.|
|Sam Hanna||LL Cool J||A former Navy SEAL-turned-NCIS Special Agent with the Office of Special Projects.|
|Oliver Johnson||Richard Cox (actor)||Member of the Gun Barrel Party who is using the alias "Roy Hale".|
|Jim Mullins||Tim de Zarn||Member of the Gun Barrel Party.|
|Leah Dewhurst||Sylva Kelegian|
|David Thompson||Jared Hillman||Professor Roy Hale's TA or Teaching Assistant.|
|Alan Sanderson||Hartley Sawyer||Member of Red Tide.|
|Brad Ross||Regan Burns|