The story is set in Republican Shanghai. Four young people with completely different life experiences come together to break into the underground world of 'Qianmen Jianghu' and solve mysterious cases. Su Zi Quan (Ning Huan Yu) is quick-witted and calls himself the 'number one master sleuth on earth.' Despite his excellent memory, he can’t recall his early childhood. His biggest weakness, however, is that he’s allergic to women. Whenever he comes into physical contact with a woman, he has to sneeze. Tang Dai Yun (Shirley Jin) is a pure-hearted and kind, yet willful rich young lady. While searching for her lost older brother, she meets Zi Quan. Joining them is the cold butler of the Tang household, Chen Yi Ming (Li Dai Kun), who possesses great fighting skills and is only gentle with Dai Yun, and Zi Quan’s childhood friend, Lu Zi Xiao (Zhu Ya), the only woman he’s not allergic to.
