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In the third year of Jianwen, Li Wu, a petty thief from Ji'nan Prefecture, saw Wang Kegong enter Nanjing with his family's fortune. He thus stole the name card of Li Dongfang, a famous clothier, to infiltrate Wang Kegong's house, in order to steal his fortune and become rich overnight. Unexpectedly, Li Mu got entangled in a dispute over the firearms of the former dynasty that revolved around the Fish Lock, and Li Mu, who was initially an outsider, became the holder of the Fish Lock, caught in the center of the whirlpool. As a child, Song Zhen, the child who rescued Li Wu from the imperial prison, has now become Lu Zheng, an Embroidered Guard and Li Wu's colleague, but they do not recognize each other; Shu Tang, a girl who was once in the same cell with Li Wu, has become an assassin, and has become a spy couple with Li Wu to complete the task. The darkness and cruelty of the dynastic strife put the feelings between the three to the test in a series of intrigues like locks. When the moment of dynasty change comes, all the battles and unresolved mysteries will come to an end....