A woman's body is found in a bed of blooming roses at the prestigious Fujikura residence. The victim is Toshio Fujikura's fiancée, and the suspects include members of the family. Reiko, who happens to be their neighbor, is fearful that her identity will be exposed. As the investigation continues, they discover that the victim's pet cat is missing, which may be a key to solving the case.

Reiko attends the wedding of Sawamura Yuri, who she cherishes like a younger sister. The groom is Hosoyama, a consultant for a family friend. When Yuri is attacked and gravely injured in her room during the party, Reiko risks her identity being revealed to help solve the case. But when the crime scene is found to be a perfect locked room, Reiko is suspected of being an accomplice.

Trouble strikes the Sawamura family again when Miyuki Sawamura is kidnapped and a ransom of 50 million yen is demanded. With no other suspects, Reiko sets her sights on Hosoyama. She takes Kageyama to the ransom handover disguised as a couple. Despite the perpetrator's traps, they inch closer to the truth, and find that the case is connected to an incident that occurred three years prior.