Non-fiction writer Katsuragi Shiho visited Shikibu Takeru at his Tokyo office several days ago. She entrusted him with her apartment key and requested him to look after her belongings if she failed to return from her trip within three days. Unfortunately, Shiho never returned even after four days, and no one knew her whereabouts. Takeru became increasingly anxious and carried out a thorough investigation, eventually discovering two witnesses who saw Shiho and a woman of similar age board a ferry to Island Kokushi near Kumamoto. Takeru embarked on a journey to find her, but the island proved to be an unfamiliar, enigmatic place with ancient traditions, a peculiar religion, and numerous unexplained deaths. Can Takeru uncover the truth about his friend amidst the odd occurrences on the island?
