Chen Ran, a low-ranking prison guard, awakens the Prison Suppression Heavenly Book System. For every day he guards the Celestial Prison, he gains a year of cultivation, and by getting involved in prisoners' karma, he can also learn peerless martial arts. On the surface, he appears cowardly, greedy, and slick, but in reality, he is patient, calculating, and ruthless when decisive action is needed. He secretly eliminates his enemies, subdues Jiang Mengli, the Holy Maiden of the Demon Cult, and repeatedly rescues Lin Wan, a renowned constable of the Six Fan Gate, while concealing his identity as a mysterious master. Facing prison breaks, a case involving stolen imperial silver, and a massacre inside the prison by the Eastern Depot, Chen Ran plays the fool to outwit his opponents, rapidly rises to the fourth rank of martial arts, firmly maintains order in the Celestial Prison, and faces a brand-new challenge as its guardian.