Shen Zhiyi, an archive restorer, runs an ancient book restoration studio called "Shiguang Pavilion" in Weilao City, Tianjin. She has been obsessed with the archives of the Republic of China since she was a child, and is especially good at deciphering hidden codes in old objects. One midnight when it rained heavily, a mysterious visitor covered in wounds and masked broke into the studio. He left behind a Republic of China iron box with a triple code lock and half a bloody fingerprint, and then disappeared into the rain. The iron box is engraved with the strange words "Keeper of Secrets Die", and inside there are clues related to the disappearance of a military and political boss thirty years ago. As Shen Zhiyi gradually cracked the code, she found herself involved in a conspiracy that spanned time and space - the owner of the iron box was a codebreaker during the Republic of China, and behind the disappearance, there was a secret intelligence network from the Japanese invasion of China. The identity of the midnight visitor, the deadly secret in the iron box, and the ensuing pursuers push Shen Zhiyi to the edge of life and death. She must decipher the triple code before dawn and find the truth hidden in the files. Otherwise, not only will her life be saved, but the dormant conspiracy may resurface and endanger more people.
