The Unending Battle(1957)

Original title: 끝나지 않은 전투

The Lysynmanovites planned to kill Lee Min Se, a prominent scientist living in North Korea, in order to take possession of his discovery. To this end, they sent Park Dong Gyun to Pyongyang. After getting a close look at life in the Democratic People's Republic of Korea, Park Dong-gyun couldn't go through with the crime and decided to tell the Korean counterintelligence folks everything. With his help, a gang of seasoned saboteurs was exposed and caught.