A mysterious sea creature appears in the South Sea of China and attacks a Chinese fleet. To appease it, the officials choose the beautiful courtesan Yin Ruiji as a sacrifice to it. Before the ceremony, Yin is attacked by a group of bandits but the young detective Dee Renjie, based on his accurate ability of deduction has foreseen her threat, saves her timely. However, Dee is arrested for that and in prison, he makes friend with a medical assistan Shatuo and the two teams up to investigate and reveal sinister conspiracy of treachery and betrayal, leading to the highest reaches of the Imperial family.