Kim Seon-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. Seon-woo works as a promising commando, but he unexpected becomes entangled in an unsavory incident after 2 years. He is demoted and is sent to a maritime police office in Gunsan city. Seon-woo's passion cools down and he slowly loses his vision as a maritime police. Then one day, Jeong-ryul, who newly formed a crime investigation section in Incheon city, visits Seon-woo and asks him to join the team..