Callen and Sam search for Arkady when crew members from the missing oil tanker used in his deal with Russia are found dead in the ocean. Their investigation also uncovers Arkady's personal connection to the ship.
A medical luminary is poisoned, and Finch and Reese must work quickly to determine the toxin's origin and find the attacker. Elsewhere, an informant gives the Internal Affairs Bureau pertinent information on Det. Fusco.