In South Korea, the formidable criminal organization known as 'Castle' reigns supreme. A lone individual, Shin Kim, a lethal assassin with the moniker 'Amur Tiger' of Korean-Russian descent, makes a daring return to his homeland. Motivated by the dying wish of his mentor, Min Sung Kang, he ventures back to the crime-infested city of Hoe-Am with a mission to dismantle the impregnable 'Castle.' As Shin Kim and his allies brace themselves for the ultimate confrontation, they risk everything in pursuit of justice and vengeance.