After a class trip to the mountains goes horribly wrong, a student who has been missing for a whole month - Junko Hayata, miraculously appears at the school. Seated on her desk, like a completely normal school day.

When unsettling things start occuring to those around her, Akiko Yuzuha, and her stepbrother - Ryuunosuke Ayase, turn to uncover the truth behind the new mystery of their childhood friend. And with the help of a detective, whether so, their old companion is still there.