Kim Sun Woo, who spent his school days as a troublemaker, decides to make a change in his life and joins the sea special attack team, which is called Poseidon. Sun Woo works as a promising commando, but he unexpectedly becomes entangled in an unsavory incident after 2 years. He is demoted and is sent to a maritime police office in Gunsan city. Sun Woo's passion cools down and he slowly loses his vision as a maritime policeman. Then one day, Jung Ryul, who has formed a new crime investigation section in Incheon city, visits Sun Woo and asks him to join the team.