Description by couchtuner for NCIS: Los Angeles Season 4 Episode 20 : 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.
Watch It Here : NCIS: Los Angeles Season 4 Episode 20 Purity
