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.

Women of differing heights are spotted at the crime scene. Kageyama suspects that elevator shoes disguised the murderer's appearance. After learning that the victim had scammed several women via dating apps, Reiko inches closer to the truth. Later, a delivery man is found dead with an item belonging to his favorite VTuber, and it's discovered that the two even frequented the same hospital.

After a delivery man falls to his death, Reiko and Kyoichiro investigate his connection to popular VTuber "Kuru Kuru-Chan," who is blamed for the murder by fans online. Kageyama assists in analyzing a mystery figure planting bugs, untouched food deliveries, and hints to the true culprit left at the crime scene. The victim leaves a note reading, "I've had enough of this world," but in what context?