Poseidon describe a story about Korean Coast Guard and Sea Special Action Team (SSAT). They struggle to defend the national from smuggling activity lead by a black group who the leader name Choi Hoi Gun.
Choi Hoi Gun without a human sense will make assassination to whoever blocking his intention include his own man. The victim or sacrifice may missing without single evidence left.
A group from National Coast Guard called Team 9 lead by Chief Director Captain Gwon assist by Kim Sun Woo, Lee Soo Young and three other members chase after Choi Hoi Gun which untill now clueless who he is?