Song Zhiyuan (played by Jiang Dongyuan), a handsome spy from North Korea, was led by the old spy Shadow, codenamed 441, and broke into an apartment in Seoul and assassinated a defector and his family. During the period, they were hunted down by the South Korean security department. After a fierce gun battle, Song Zhiyuan and others escaped by chance, but he was abandoned by his superiors for being a traitor. On the other hand, the failure of the operation led to the dismissal of Lee In-gyu (played by Song Kanghao), the captain of the South Korean action team. He had to open a detective agency and support his family by collecting money to track down the escaped Vietnamese bride. Soon, Kim Jong-il and Kim Dae-jung had a historic meeting, and the situation between North Korea and South Korea eased. Six years later, Lee In-gyu met Song Zhiyuan in a Vietnamese factory. He hoped to catch Zhiyuan and the mysterious shadow to make a lot of money, and Zhiyuan also wanted to use In-gyu to wash away the charge of his own betrayal. The two lived under the same roof with ulterior motives, and as they got to know each other better, their ideas gradually changed...