"Purity" Pictured: LL COOL J (Special Agent Sam Hanna). When cyanide in a communal water jug lethally poisons a lieutenant and leaves a Navy pilot in serious condition, the NCIS: LA team investigates whether this is an isolated incident or an early test for large-scale water contamination, on NCIS: LOS ANGELES, Tuesday, April 9 (9:00-10:01 PM, ET/PT) on the CBS Television Network. Photo: Cliff Lipson/CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved.