During the Shaoxing period of the Southern Song Dynasty, Lu Qingci, the daughter of a prison family, disguised herself as a man and sneaked into the county government to serve as jailer in order to investigate her father's unjust case. In the dark prison, she met Zhao Heng, the fallen prince who was falsely accused of treason. At the boundary between crime and punishment, the two men jointly uncovered a major illegal salt case that ran through the government and the public.
