At the age of 19, Prince Qi, Pei Yanzhi, was ordered to defend the country against the invasion of Fan Yan Na. With his innate military prowess, Pei Yanzhi turned the tides in their favor but his army was ambushed and defeated in the final Battle of Hong Valley, costing them the victory. As he barely escaped death and returned to the palace, the cunning and power-thirsty Prince Yun questioned his defeat, forcing Pei Yanzhi to relinquish control of the military. Realizing that Prince Yun was coveting the imperial power in the act of supporting the enthroning of the young emperor, Prince Qi came to a tacit agreement with the young emperor and decided to withdraw himself from courtly affairs. Meanwhile, he embarks on an undercover search for the truth behind his crushing defeat with the alias, Pei Zhao.
While Pei Zhao is off to investigate a case surrounding missing government fund set aside for the calamities, he meets the young and determined detective Su Ci in Qingshui County. Pei Zhao starts to work with her, attracted by her aloof character and incredible deduction skills. Along the way, the two came to know Xie Beiming, the young master of Yunshan Manor, and Dong Rushuang, the daughter of the Poison King. Forming a four-member detective team, they work together to solve mysterious cases and get closer to lurking dangers. Su Ci’s identity is exposed while the secrets of the palace are eventually uncovered, embroiling the team into various awaiting challenges.