After an ex-gangster named Wang-jae (Ahn Gil-gang) is killed by a gang of punks, his four childhood friends come back together for the first time in nearly twenty years. Each of them has gone different ways, Tae-soo a detective, Pil-ho a powerful mobster who once worked with Wang-jae, Seok-hwan (Ryu Seung-wan who also is the director) a reformed mobster and his brother Dong-hwan a math teacher. They reminisce about times gone, their mischivous teen years, and a pact they made on a school picnic. Young Wang-jae made a snake tonic and buried the bottle, vowing that twenty years later they would all gather and drink it after they became wealthy men. After the funeral both Tae-su and Seok-hwan deal with their grief by investigating the murder. While on the case Tae-su is attacked by a massive gang of youths, who use baseball bats, hockey sticks, and even yo-yo's as weaponry. Tae-su barely escapes with help from Seok-hwan, and the two team up, taking their revenge on the crazies the next day. After hunting the gangs down one by one and beating the tar out of them, they discover that Wang-jae's death wasn't a random attack but actually planned. After capturing one of the murderers, they find out that Wang-jae was actually targeted by his once good friend Pil-ho who he fell out with during negotiations to turn their city into a tourist district. After giving the murderer protection so he can testify against Pil-ho, the killer killed by an assassin who douses him in gasoline and lights him on fire. Tae-su, realizing theres no legal way to take Pil-ho down, faces off with him, but is beaten by his bodyguards, and only left alive out of some sort of pity. At the same time Seok-hwan and his mother and brother are hit by a truck. Seok-hwan survives but his family is dead, killed by Pil-ho's men. The two nearly destroyed men meet at the funeral, where Wang-jae's widow who is also Pil-ho's sister gives them information that they can use to seek their revenge. The two friends, no longer bound by the law, storm Pil-ho's fortress during the negotiations for a casino, only armed with a pair of wooden bokken. They fight their way through a sea of cooks with butcher knives, a long hallway lined with bodyguards, a man with a katana and finally four of Pil-ho's elite guards with hands and feet. Pil-ho, having bludgeoned the president he was meeting with after being insulted by him, faces the exhausted men, and easily crushes both of them. He stabs Tae-su, ignoring Seok-hwan who binds the katana to his hand with bandages and stabs Pil-ho through the chest, killing him. Tae-su bleeds to death, and Seok-hwan, merely kneels among the carnage they have wrought, uttering only "fuck."
The film ends with the young versions of themselves walking back from the School Picnic, talking about their future. They talk about coming back for the snake tonic when they become rich men. "Don't worry" one of them says "we won't amount to much anyway!"