The story is set in winter, at Seibunka Private Academy in Asahikawa, Hokkaido. The protagonist, Subaru Sakaki, and his childhood friend, Honoka Takamura, are excited as the final Christmas party of their school life approaches. However, their joyful days are shattered by the sudden news that their classmate Miyabi Yashiro and homeroom teacher Asuka Yuri have been murdered. And their close friend Kazuha Shinozaki has been arrested as the murder suspect. Believing in their friend’s innocence, Subaru and Honoka begin their investigation to uncover the truth behind the incident, but behind the scenes, someone deeply connected to a “certain secret” of theirs is pulling the strings.
