In the 23rd year of the Republic of China, "Linzhou", a commercial port in the south of the Yangtze River, was divided between three wealthy families. On the surface, it was a prosperous scene of silk, medicine, and shipping, but secretly it was opium, business marriages, and family strife. The heroine Shen Yanqiu was born in a declining medical profession. With her "poison doctor" skills that can save people and kill people, she started a shady diagnosis and treatment business in Linzhou's upper class. She was secretly protected by Gu Huaiyan, Gu's eldest son, when she was young. She kept this feeling in her heart for many years, but was forced to get involved in the Gu family's infighting again during a wealthy family's birthday banquet drug case. The Gu family is setting up a trap step by step for the sake of family business and reputation. While Shen Yanqiu is investigating the truth about old cases and serial poisonings, between secret love and suspicion, Shen Yanqiu and Gu Huaiyan go from testing each other to playing chess side by side.
