Detective LIN is in charge of a case that appears to be an accident. The site of the incident has many features in common with a scene from A Study in Scarlet, a Sherlock Holmes novel. In another part of town, four friends have been in a detective club since their college days. When the detective club president and owner of a detective bookstore, GAO, become involved in a murder case, the other three try to be helpful, but they all seem to harbor a hidden secret of their own. As Detective LIN delves deeper into his case, a series of seemingly unrelated events all end up pointing toward the club members’ dark pasts.