In the twenty-fifth year of the Republic of China, thick fog locked up the city in Jinmen. Rich businessman Ye Shian died suddenly and mysteriously in a locked study room. The scene was strangely clean and tidy. Only a trace of indigo velvet between his fingernails became the only suspect. Patrol room consultant Lu Chenzhou intervened in the investigation, but found that the case involved the famous actress "Jade Butterfly" who fell from a building three years ago. Gu Qingwu, the family doctor of the deceased, was calm and mysterious. He was both Ye Shian's sponsor and the sister of "Jade Butterfly". Her appearance made the clues even more confusing. From a page of "On Salt and Iron" that was torn out in the study, to the housekeeper who fell to death in Jinhe River, and then to the "old story of a butterfly falling on Dangui Street" pointed to by an anonymous letter, Lu Chenzhou pursued the case in the fog, gradually uncovering the intertwined puzzle of antique smuggling, grievances between wealthy families, and revenge for old cases. Every step of exploration is accompanied by danger, and the eyes in the dark follow you like a shadow, and behind that touch of indigo lies a shocking secret that can overturn Jinmen.
