In Berlin, the German capital, a failed arms deal has heated up the confrontation between the various forces of North Korea and South Korea. North Korean ambassador Li Xuexiu (played by Li Qingrong) and spy Biao Zongsheng (played by Ha Zhengyu) discovered that another cold-blooded spy from the motherland, Dong Mingxiu (played by Liu Chengfan), appeared in Berlin. The regime change filled them with ominous premonitions after years of wandering overseas. During this period, Zongsheng had to follow the instructions of the party to monitor the whereabouts of his wife, the ambassador's personal translator Lian Zhenxi (played by Jun Ji-hyun). On the other hand, Minister Kang (played by Han Seok-kyu), the head of the South Korean intelligence agency, who suffered setbacks in the pursuit of the arms trade, was unwilling to fail and continued to track Zongsheng's whereabouts. After the ambassador's defection plan failed, Zongsheng learned of Dong Mingxiu's true purpose in coming to Berlin. In order to avoid becoming a victim of the power struggle and the target of purging, he had to flee with his wife...