The film follows the lives of four childhood friends: Joon-seok, the leader of the group whose father is a powerful mob boss; Dong-su, whose father is an undertaker; class clown Jung-ho; and Sang-taek, who was an exemplary student. As children, they play together and sell sexually explicit pictures. In high school, they become smitten with the lead singer of a girl band their age. Joon-seok invites the band to a party at his house, where Sang-taek receives his first kiss from the lead singer, Jin-sook.
In school, Joon-seok and Dong-su get in trouble after a confrontation with a teacher; they apologize and only receive a light suspension. During an outing to the movies, Sang-taek catches the eye of a school kid he had picked a fight with earlier. Joon-seok and Dong-su fend off a whole rival school while Jung-ho protects Sang-taek. Dong-su smashes the school’s glass cases with its awards and trophies and drops out of school. After graduation, Sang-taek and Jung-ho go to college but the others do not.
A few years later, Sang-taek and Jung-ho return to find Joon-seok married to Jin-sook. He is suffering withdrawal symptoms and is abusive towards his wife as a result of being addicted to philopon. Later, he recovers from his addiction, divorces his wife, and mourns his father’s death. He assumes his father’s role as a crime lord, working under Hyung-doo. Dong-su becomes a mobster with a rival organization, led by Sang-gon.
Joon-seok, Sang-taek, and Jung-ho remain close, drinking, singing karaoke, and eating galbi together. After Dong-su causes Joon-seok’s boss to be imprisoned, a rogue assassination attempt, headed by Doruko, is led against Dong-su without Joon-seok’s knowledge. The attack fails, and in retaliation, Dong-su mounts an attack on Joon-seok’s fishing facilities, during which many of Joon-seok’s men, including Doruko, are killed. Joon-seok talks to Dong-su and asks if he would like to accompany him to see Sang-taek off to America. Dong-su says no. He asks Dong-su to leave for Hawaii until the situation returns to normal, but Dong-su refuses, telling Joon-seok that he should be the one to go. After Joon-seok leaves their meeting, Dong-su reflects and asks one of his men to take him to the airport. However, outside his car, he is stabbed to death.
A few years later, Sang-taek returns to South Korea upon finishing his study abroad. Jung-ho explains that Joon-seok’s gang sent him into hiding abroad. After two years, he was unable to stand the hiding any longer. He was caught in a foreign bar, found with severe self-inflicted wounds. Joon-seok stood trial for Dong-su’s murder and pleaded guilty to ordering Dong-su’s death.
Sang-taek visits Joon-seok in prison, and the two talk like old friends. Sang-taek asks why he pleaded guilty in court. Joon-seok simply replies, “Embarrassment. Me and Dong-su are mobsters. Mobsters shouldn’t be embarrassed.” Sang-taek and Joon-seok part ways, with Sang-taek promising to visit every month. The film ends with Joon-seok walking to his fate in prison life, and Sang-taek reflecting on the past when they were all children, when they were all good friends.