A small detective office in a non-descript back street shopping center, there is Goro Asami, a private detective, competent in his job, with business going well, but not well enough to live in wealth. There is Otomi Kiyosato, a student of Siratori High and the founder of the "Beauty Private Detective Club, one of the stranger clubs in that school, being an absolute pain in the ass by claiming to be Goro's assistant and inviting herself to his office enough to absolutely drive him up the wall.
During this period of relative bliss, an unexpected incident shatters the peace of Siratori High. Mari Kitagawa, the chief manager for the Creative Literature Club, is found dead with massive doses of tranquilizers and sleeping pills in her body. From the location of the body and the means of her death, the police initially declared this to be a suicide, but by the following day, they abruptly change their stance by issuing a cryptic statement that "Her death was not from suicide." Rumors spread throughout the high school like wildfire, and Otomi and her fellow detective club members began investigating the case. Goro also begins investigating this strange case, after being hired by the victim's father. With Otomi's cooperation, each step of the case gradually comes to light. Yet, before the case could be determined to be murder or suicide, Tomoko Andou is found raped and murdered at the thicket of the high school's rear compound. What is going on? Are the deaths related? Who wrote that mysterious notice, "Who's next?" on the board?