For years, O has lived isolated in the world of professional killing. His intensely disciplined regime forbids him any contact with others, and the death of his lover has served only to force him further away from the world around him. Tok, however, is a flamboyant newcomer to this secretive world. Chasing the thrill of the hit, he is driven to become the number one, but there is a significant obstacle: O, and his fierce dedication. Using O's part-time housekeeper, Chin, as a way to get to O, Tok begins his campaign. Soon, Chin is dragged into their dangerous world and, as Tok challenges his elusive rival to duel, Agent Lee at Interpol gets closer to finding O.