In Shanghai in 1940, Chen Jiaping, an underground member of the Communist Party of China code-named "Plum Blossom Four", met his former fiancée Zuo Shuangtao at a critical moment when he was almost exposed when he was on a mission. At this time, Zuo Shuangtao was already an agent of the Kuomintang military command. He failed in his assassination mission and was also looking for a way out of trouble. The two people, who did not know each other's identities as agents, relied on their tacit understanding to cope with the Japanese's rigorous interrogation, and finally passed the test as a couple. Suspicious of the two pretending to be lovers, the Japanese immediately forced the two to get married, and Zuo Shuangtao also used the trick to work in a commercial bank. After that, Chen Jiaping completed the task while dealing with the identity crisis that could not be eliminated, and also tested Zuo Shuangtao's true identity! The struggle became increasingly cruel, and finally Jiaping discovered that Shuangtao was the "Five of Hearts", an agent of the military command, and Zuo Shuangtao also discovered that Jiaping was the "Four of Clubs", the CCP agent. Through an in-depth understanding of the anti-Japanese attitudes and contributions of the two parties, Zuo Shuangtao finally chose to fight with Chen Jiaping, inspired by his communist beliefs. They have gone through many tests, completed arduous tasks under the leadership of the party organization, and embarked on a new journey together.
