Secret Reunion (2010) on Netflix

Plot summary

Song Ji-won is one of many North Korean agents living in the South under ordinary cover. Pyongyang orders him to kill a relative of Kim Jong Il who has written a book the North condemns. Lee Han-gyoo, an officer of the National Intelligence Service, learns of the plot and closes in with his own team, without telling his superiors. The operation fails, and the agency dismisses him as the one to blame. Ji-won gets away but is suspected at home, so he can neither return nor defect while his wife and daughter stay in the North. Six years later he works on a building site, while Han-gyoo makes a living as a private investigator. A chance meeting puts them face to face.