Long ago, a warlord sought a fabled key that would grant the power to rule the world. This pursuit fractured countless lives as men killed one another. The Tao Masters, sworn to refrain from human battles, watched in restraint—until one, Heuk-woon, Jung Doo-hong, was horrified by the atrocities and intervened, killing the warlord and seizing the key to “bring peace” through power. The remaining six Tao Masters imprisoned him in an underground dungeon and took turns guarding the key until the true Arahan arrived.
In the present day, a clumsy auxiliary police officer Sang-hwan, Ryoo Seung-bum, is accidentally struck by an energy attack from Eui-jin, a prospective Aruchi (female Tao master). She then leads him to her father Ja-woon, Ahn Sung-ki, the Maruchi and guardian of the key. They sense Sang-hwan carries an unusually strong Qi and offer to train him, a chance he eagerly accepts in hopes of finally earning respect instead of laughter and blows. After some initial missteps, he begins to show remarkable skill and potential.
Meanwhile, construction crews uncover Heuk-woon’s dungeon, and the ancient terror—who has survived for centuries by drawing on dark Qi—sounds the hunt anew. Heuk-woon’s ruthless pursuit pushes him to drain the life energy of those he encounters, leaving only Eui-jin’s father and Mu-woon, Yoon Joo-Sang, still standing in his way. In a bold rush to seize the key, Heuk-woon targets the masters one by one, tightening the noose around the fragile balance of power.
When Heuk-woon finally breaches the Tao school, Eui-jin and Sang-hwan struggle to halt him. Sang-hwan lands a lucky hit with a small boulder, and Mu-woon gives chase before meeting a fatal sword thrust. Ja-woon then explains the dark history of Heuk-woon and entrusts each of them with half of the key, setting the stage for a hurried escape from town in a waiting car. Eui-jin, unwilling to abandon her father, decides to push forward with Sang-hwan, and he wrestles with his own anger before choosing to ride on.
The final confrontation erupts in the city museum, where Heuk-woon manages to steal their halves of the key, yet is ultimately defeated by Sang-hwan’s renewed resolve and growing power. The key—an image of a dragon—seeps back into the ground, leaving the city with a sense of uneasy peace and new possibilities. The thief from the opening scenes is once again pursued, this time by a team that includes Sang-hwan and Eui-jin, who face their own rough edges and surprising synchronicity as a duo. The closing shot lifts the camera toward the skyline, with figures leaping across rooftops as the city continues to move forward.
