Having previously focused his attentions on films about the experiences of Koreans in contemporary Japan, Korean-Japanese filmmaker Yoichi Sai reverts to the Korean reading of his name (Choi Yang-Il for this moody underworld thriller about a mysterious loner in search of his long-lost twin. Adapted from the popular Korean manga of the same name, Soo follows the journey of a wanted man named Tae-Soo, who has spent nineteen years attempting to locate his missing sibling Tae-Jin. Tae-Jin was snatched away when they were just young boys, yet Tae-Soo is convinced that his brother is still alive almost two decades later. Pursued by both the police and the most dangerous gangs in Korea, Tae-Soo does ultimately manage to find Tae-Jin, though the moment they are reunited Tae-Jin is suddenly killed. In the aftermath of Tae-Jin's death, Tae-Soo assumes his identity in hopes of tracking down the killer. The fact that Tae-Jin was a policeman doesn't make pulling off such an elaborate ruse very easy, though Tae-Soo does manage to play the part long enough to access his brother's police files and discern that Tae-Jin's kidnapper and killer are one in the same. Now, as Tae-Jin embarks on a quest for revenge that takes him directly to the top of the gangland hierarchy, the resulting violence plays out with all the power of a Greek tragedy.