Ruko and her younger sister Sara find themselves at the "Bookstore in the Rain" once again. They must discover what the mysterious bone dragon Mr. Yondakure is planning, as he has developed a habit of destroying bookstores and libraries. The cunning dragon uses time magic to steal the precious rainwater and destroy the "Bookstore in the Rain". And Sara suddenly disappears... Can Ruko find her sister and save the magical book repository from the villain?
