Uimin, trapped by the rigid walls of social hierarchy, begins a dangerous gamble to break through his limits! Set in the mid-Goryeo period, a time when underground gambling fights (*nae-gi subak*) were rampant, Uimin is known as the best brawler in his village and infamous as the "Mad Dog." Despite his humble origins, he dreams of becoming the greatest military officer in Goryeo. However, as a lowborn commoner, he has no legitimate path to achieve his ambition. His only option is to participate in rigged matches, deliberately losing in exchange for money to satisfy the whims of the nobility. One day, during yet another fixed match, his opponent taunts him: "You filthy slave, lower than a dog!" He’s supposed to swallow his pride and lose, as always. But this time, something snaps. When he comes to his senses, the match has ended in his victory. This unexpected outcome sets Uimin on a perilous and uncharted path, filled with challenges he has never faced before. Can Uimin overcome the odds and achieve his ultimate goal of becoming an unparalleled military officer?