Early Republican China, Sihai county. Meng Guofu, the richest man in the county, has divided his wealth between his two sons, Shaoqiang and the younger Shaoyun. When Shaoqiang is beaten to death one night with a stool, Shaoyun (Patrick Tam) is arrested and, with blood on his hands, admits his guilt. Meanwhile, "the world's greatest private detective" Ka Naiji (Guo Tao) - born and raised in the local Hibiscus Garden whorehouse and interested solely in making money - receives an anonymous message asking him to fight for Shaoyun's innocence. His liaison, until the case is solved, is to be Meng family doctor Zhou Ziru (Fan Lei), who assigns his niece Linlin (Cecilia Han) to help Ka, as she already knows the details of the case and happens to be a martial arts expert. Ka interviews the imprisoned Shaoyun who says his brother asked him to sign over his half of the inheritance and, when he refused, he fell unconscious, waking up to find his brother dead and a bloody stool in his hands. Ka realises Shaoyun was drugged and that the unrecognisable dead body may not be Shaoqiang's after all. Shaoyun says he wants to see Yu Na (Ju Wenpei), Shaoqiang's grieving widow, so Ka and Linlin journey to the countryside to meet her. Then the case develops a surprising twist when Ka discovers that Shaoqiang willed his share of the inheritance to an adopted son in Korea.