The bride is behind locked doors (S01E11)

Reiko is at the wedding of Sawamura Yuri, whom she holds dear as a younger sister. The groom, Hosoyama, is a consultant connected to a family friend. During the celebration, tragedy strikes when Yuri is assaulted and seriously hurt in her room. Determined to uncover the truth, Reiko puts her own anonymity on the line to assist in the investigation. However, things take a turn when the crime scene is discovered to be an impossible locked room, leading to suspicions that Reiko may be involved in the crime.