Twenty years ago Onodera Fuyuha went missing on a school trip. One day her former classmates Inoue Keiko, Akiyoshi Miya and Kawano Takako receive an email which is supposed to be from Onodera. With two other classmates Sabashima Yutaka and Higashihagi Koji they try to find out more. Before long, misfortune starts to befall the reunited classmates.