The Dou family of Foshan is an affluent family that owns and runs Sheung Chun Tong, the largest traditional Chinese apothecary in town. When an epidemic occurs in Foshan and the shop's medicine is found to be the cause, the shop owner is accused of murder and is imprisoned. In order to help release her father, the family's only daughter, Dou Gaai-kei, sets out to investigate.