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.

While investigating the murder of a real estate tycoon, Reiko examines an erased dying message, a bloody trophy, and a cord yanked from the curtains. Without proof, however, she reaches a dead end...until savage butler Kageyama emerges to solve the mystery. Reiko and Kyoichiro think outside the box to trap the murderer, peek inside the victim's mindset, and end a chain of events fueled by revenge.

With Kageyama as her chauffeur, Reiko and her friends visit a crowded summer festival, where a cracked smartphone is discovered. Its owner was poisoned in his apartment, and he died wearing nothing but briefs. Three women the victim dated simultaneously on a matching app fail to match the height of a suspect seen exiting his residence, which leaves Reiko puzzled at the true culprit's identity.