When an unknown toxic gas strikes Seoul in an unprecedented act of terror, Yong-nam has just met Eui-ju from college by chance at his mother's birthday banquet. The city falls under sudden noxious gas attack and together, they must escape the panic-stricken city.

A corrupted customs officer, Choi Ik-hyeon, faces losing his job. Then, his life turns around as he meets ganster Choi Hyeong-bae who has connection with the Yakuza. They quickly form a partnetship; Hyeong-bae helps Ik-hyeon set up a business with the money from drug trafficking while Ik-hyeon lobbies for his partner Hyeong-bae. As the government declares war on crime, however, their partnership begins to crack.

Disgraced by the ill-fated drug sting, ex-cop Dae-ho lives in Busan as a unofficial sheriff and looks after the town. Meanwhile, new businessman in town Dong-jin wins townspeople's favor to start a beach resort, which becomes a huge hit. Dae-ho recalls that Dong-jin was somehow involved in the drug sting and begins an investigation, suspecting that he's also involved in a drug case that took place recently.