The prodigy Iria Akagami has been compelled by her family to dwell in a mansion on the secluded Wet Crow's Feather Island with just a handful of maids due to a mystery ailment. To keep herself amused, Iria invites computer genius Tomo Kunagisa and her nameless helper, talented fortune-teller Maki Himena, famed artist Kanami Ibuki, academic scholar Akane Sonoyama, and renowned cook Yayoi Sashirono to stay as guests in her house. These visits proceed normally until one of the visitors is found gruesomely killed in the middle of the night with no indication of the identity of the perpetrator or a plausible reason. As the killer remains at large, tensions escalate among everybody on the island, including Tomo's helper.