Chul-min lost his mother when he was young. He now lives together with his father, the chief investigator of the town, and his half-bred dog. Ever since he was a boy, the locals and his father have called him "Mutt Boy" because he roamed around the neighborhood asking for food like a stray dog. Mutt Boy calls his half-bred police dog "Mutt Boy" as well and they go everywhere together as if they are brothers. But then one day, other members of Mutt Boy's high school soccer team steal his dog and eat it. Chul-min goes after them to seek revenge, but Chul-min's father pops up at the scene and takes him away.
A few years later, Chul-min drops out of high school and lives day by day doing nothing useful. Then one day, some street bandits (aka Miryang Junior 'Klub', MJK) who got kicked out of high school and have nothing going for them like Chul-min, challenge Chul-min to a duel. After the match, Chul-min is victorious and he begins to hang out with the MJK boys.
One day, Chul-min's friend Big Dough gets beaten up by the neighborhood thugs and falls victim to the tyranny of Mr. Oh Duk-man who wants to build an expressway by evicting people from their homes. Although he's simple-minded, Chul-min knows deep down what's right or wrong and begs his father to arrest Oh Duk-man. However, his father just gives him a cold shoulder and merely responds that he’s on the case.
Chul-min can't wait any longer and finally decides to punish Oh Duk-man’s henchmen. So together with his MJK boys he goes to look for Oh Duk-man's street thugs and finds out that the leader of the thugs is none other than Jin-mook, the one who ate his dog, back in high school. To avenge his friend Big Dough and his dog, he fights Jin-mook and the thugs, but all of them get arrested after all.
Chul-min and Jin-mook end up getting into a final showdown to settle things once and for all as the one who loses takes the wrap for everything. Chul-min and Jin-mook are stripped down to their underwear with a towel wrapped around their mouths. Then like two dogs at a dogfight, a gruesome fight begins.