Mei Shiqi, a junior agent in the Yu Dynasty's Secret Guard, teams up with Leng Moyan from the Imperial Inspection Bureau to investigate a mysterious palace murder. Despite initial distrust, they work together to uncover a dangerous conspiracy threatening the kingdom.

Lin Dawei, an assistant to the county government, needs money to feed his family. Lin is persuaded by his colleague Lu Qian to steal Jin Mantang's gold. Ten years later, the emperor's eldest son was born, the emperor pardoned the criminals, and Lin Dawei returned home. However, things did not go well in his hometown. Jin Mantang joined forces with smugglers to kill thousands of people. The swordsmen that Lu Qian sent to kill Jin Mantang were destroyed, and Taiping was in danger.

At the beginning of the Tang Dynasty, a rain prayer ceremony was organized to alleviate drought, but it was used by those with intentions to create a mysterious case of "Thousand-Headed Demon" appearing. The intelligent and extraordinary death row inmate Dugu was appointed by the Holy Emperor to investigate this case, but unexpectedly, it involved even greater conspiracies.