Wealthy heiress Reiko Hosho leads a double life as a novice detective. One day, an incident erupts at a birthday party she attends with friends from her college days. The victim is one of her old classmates, and Reiko's friends are labeled as suspects for matching the attacker's description. Stirring in confusion with only 20 minutes to solve the case, a man suddenly appears to reveal the culprit.

Mystery butler Kageyama concocts a peculiar plan to catch the criminal lurking in a luxury hotel, after which Reiko and her friends realize the hidden complexity of their own emotions. Reiko then tackles the murder case of a real estate tycoon. Each of the victim's relatives harbor suspicious motives to kill, but a single photograph proves essential in accelerating this perplexing investigation.