Ren Nakazato has just entered high school. On only his second day, he heads to the old school building to check out the Top Exploration Club, a rumored group dedicated to investigating the school’s seven wonders. There he meets three other first-year students, all drawn by the same curiosity. When no senior club members appear, the four decide to leave and disband the attempt—only to discover they cannot escape. A supernatural force has sealed them inside the old building. A cryptic message left in a classroom reveals the terms of their imprisonment: before sunrise, they must solve every one of the school’s seven mysteries. If they fail, they will remain trapped in the night of April 7 forever. As they work through the puzzles, each solved mystery causes the number of characters in the supernatural entities’ names to increase, and with that growth comes escalating danger. The story blends occult horror, a boy-meets-girl dynamic, and a youthful mystery, following the four students as they race against time, uncover hidden secrets about each other, and confront the true nature of the anomalies haunting the school. The manga is an adaptation of the novel Nanoka no Yoru o Nukedashite and is complete in two volumes.