In the future, during the Yan Dynasty, "accidental" deaths of maids occurred in the palace. Lin Xiaotang, the sister of private detective Lin Zhaozhao, also died among them. The official verdict was that he "stumbled and fell into the water", but Lin Zhaozhao discovered the secret code left by his sister before her death and suspected suicide. In order to investigate the truth, she entered the palace disguised as a palace maid and awakened the "Palace Unsolved Case Detective System" (professional type, which can analyze traces, restore scenes, and identify lies). In the process, she met Shen Yanzhi, a tolerant and upright palace guard. The two worked together to uncover the truth behind her sister's death, and gradually revealed that the noble concubine Su Wanqing had designed a conspiracy to kill the palace maid who knew about it in order to compete for the throne. In the end, Lin Zhaozhao used the evidence restored by the system to bring Su Wanqing to justice, avenge his sister, and also uncovered the power corruption hidden in the palace.
