In the context of the Chongqing spy war in 1943, Su Qingyuan, a female translator and telegraph operator codenamed "Nightingale", was forced to have a "business marriage" with Lu Jingnian, a military agent she had never met before (fitting with the popular "Marriage First, Love Later" track) in order to complete her mission. The two live under the same roof. On the surface, they are a "contracted couple" who do not trust each other. In fact, they each have hidden secrets - Su Qingyuan is an underground party, and Lu Jinnian is a patriot lurking in the military command. When deciphering a Japanese military secret message, Su Qingyuan discovered that the code was highly consistent with an ancestral dialect dictionary of "Sichuan Language" passed down from her family. Lu Jinnian also happened to hold the same dictionary. The two used dialect code words (such as "Bashidban" corresponding to "mission safety", "Zhaguai" corresponding to "there is an ambush") to find out each other's identities. From testing each other to working together to break the situation, they protected their homeland and love in troubled times.
