During the Qingli Era, troubling affairs brew underneath the prosperity and stability of the Northern Song Dynasty. Separatist regimes are secretly operating in the capital city of Dongjing, spying on the secret affairs of the Song Military. To avoid war and protect the peace between its people, the Northern Song uses the name of "Mi Ge" (Secret Cabinet) to train young spies. For a variety of reasons and whether willing or unwilling, these six become the Seventh Room of Mi Ge after strict selection and examination: cunning and intelligent Yuan Zhong Xin; beautiful and resourceful Zhao Jian; Xiao Jing, who can’t even kill a fly; never-lying Wang Kuan; antisocial Xue Ying; and admirer of beautiful women, Wei Ya Nei.

Upon first entering the school, each acts out of their own self-interest, making a mess of their surroundings and causing headaches for their teachers. After going through a series of life-and-death missions, the previously ignorant boys and girls gradually mature and form bonds with one another, devoting their determination and loyalty to defending the peace. Burying their names, they become unknown legends within the river of history.