The story is set in Republican Shanghai. Four young people with completely different experiences in life 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 and kind-hearted, but also willful rich young lady. While looking for her lost older brother, she meets Zi Quan. Joining these two is the cold butler of the Tang household Chen Yi Ming (Li Dai Kun) who has great fighting skills and is only gentle to Dai Yun, and Zi Quan’s childhood friend Lu Zi Xiao (Zhu Ya), the only woman he’s not allergic to.