After finishing their final exam, students are about to leave for summer vacation. Akko discovers in the library a secret room that leads to the chamber of Horologium, hidden in the basement of the school. A clock that uses a forbidden magic to manipulates time, one of the seven wonders of the Luna Nova Academy. Akko and her friends end up trapped in a time loop, reliving the same day over and over and over and over. Will they be able to escape this time paradox and solve all of the mysteries of the Academy ?