In Shanghai in 1940, Chen Jiaping, a Communist underground operative codenamed “Plum Blossom Four,” runs into his former fiancée, Zuo Shuangtao, while carrying out a mission. He is on the verge of being exposed, while Zuo has just failed an assassination attempt and is also searching for a way out. Neither knows the other is an operative, but drawing on the rapport they shared years ago, they withstand the Japanese security forces’ stringent questioning and narrowly get through by pretending to be a couple. Suspecting their act is a cover, the Japanese force them to marry, and Zuo takes the opportunity to get a job at a trading company. From then on, Chen must complete his missions while dealing with the lingering danger of exposure and probing Zuo’s true identity. As the struggle grows ever more brutal, Jiaping discovers that Shuangtao is a Military Statistics Bureau agent codenamed “Red Heart Five,” while Zuo discovers that Jiaping is a Communist operative codenamed “Plum Blossom Four.” After gaining a deep understanding of both parties’ stances and contributions in the war against Japan, Zuo is moved by communist ideals and ultimately chooses to fight alongside Chen Jiaping. They weather one trial after another, complete difficult missions under the Party’s leadership, and embark on a new journey together.
