On a snowy school day like any other, classmates and childhood friends Hiroshi and Mizuki arrive at school to find the campus eerily empty. Before long, they find themselves trapped inside with six other friends, and even stranger, all the clocks have stopped at a very specific moment—the exact time when a former classmate jumped off the school roof to their death three months earlier. It turns out that this departed friend is their way out of their current predicament and may even be among their group...but no one can remember who it was that took their life on that sad day. The students must face themselves and their past memories to piece together the identity of this suicide victim or risk a similar fate—with their lives lost and forgotten inside these frigid school walls.

A regular school day has turned into a chilling horror as Hiroshi, Mizuki, and their friends find themselves confined within the frigid walls of Seinan Gakuin. No one can seem to remember who took their own life at the school festival, but whoever it was is keeping them captive. And to make matters worse, the eight trapped classmates become seven when Mitsuru suddenly disappears with only a trail of blood in his place. Now they have even more reason to solve the mystery of their bizarre circumstances—because if they don’t, the only thing they may be leaving is this mortal coil…

充、清水さん‥‥校舎から2人の仲間が消えた。残されたのは深月・鷹野・菅原・リカ・景子・昭彦。この中に、“あの日”自殺した生徒はいるのか？　戸惑いもがく彼らを、更なる悲劇が襲うーー!!

雪の降る登校日、校舎に閉じ込められた8人の高校生。その半分が姿を消し、残った鷹野、菅原、景子、深月。彼らの中に学園祭の日“自殺した生徒”はいるのか？　凍りついた真実は、陽光の下にーー。メフィスト賞受賞の青春ミステリー、遂に完結!