The Chinese Gongan literature, in which various bizarre stories of judgments of court cases and legends of judicious magistrates have been narrated, dates back to ancient times. While most Gongan works are full of narratives of deified abilities of officials in charge of lawsuits and beliefs in karma and reincarnation, they lack mysterious plots, exhilarating detective skills and criminal investigation processes that one usually encounters in the western detective stories. Shi wu guan (Fifteen Strings of Cash), a legend of Ching Dynasty, is a special Chinese Gongan opera--the occurrence of its criminal cases consists of numerous coincidences, and its criminal investigation process demonstrates strong detective characteristics. In this paper the riddle formation and unraveling processes in Shi wu guan are analyzed to illustrate the unique and generic features of this work among the traditional Chinese Gongan works.