Secret Reunion

Secret Reunion Hangul hanja RRUihyeongje lit. Sworn Brothers or Blood Brothers is a 2010 South Korean spy thriller film directed by Jang Hoon, and one of the highest grossing Korean films of 2010.

Jiwon is one of numerous North Korean undercover spies living in South Korea as ordinary citizens, until hes called to fulfill his mission the assassination of Kim Jongils second cousin who wrote a book that the North Korean government deems as a great betrayal to the Fatherland. However, one of his fellow spies, Taesoon, betrays his orders by switching his allegiance to South Korea, and Jiwon mistakenly becomes the target for both countries.Lee Hangyoo is a dedicated agent of the National Intelligence Service NIS who tries to foil the hit. Despite having insider information, he doesnt notify his agency superiors, and only involves his team in the mission. Unable to prevent the assassination, and with the loss of his fellow agents in a gun fight, he becomes the sole scapegoat for the agency and gets discharged. ........

Source: Wikipedia