When a mysterious stone falls from the sky, the young boy Riku is swept into a time‑traveling adventure with Stella, an alien explorer who carries a magical Quest Book. Riku’s classmates Kirara and Ginga soon join them, and together they are transported back to the Cretaceous Period. Their mission is to discover the origins of a fossilized dinosaur egg, which soon hatches in their care. Armed with the Quest Book and a small hand‑held device that feeds them real‑time paleontological facts, the children explore a prehistoric world filled with towering sauropods, diving into ancient oceans, and encountering fearsome predators such as Tyrannosaurus rex. They befriend a baby T. rex and ride docile herbivores, all while learning about dinosaur behavior, evolution, and the environment. The story also includes sidebars with scientific explanations about topics like ammonites, tectonic drift, and the eventual meteor impact that ends the age of dinosaurs. The main characters—Riku, the energetic protagonist; Kirara, who becomes a nurturing surrogate mother to the baby dinosaur; and Ginga, the dinosaur‑obsessed but clumsy friend—each have distinct roles in the adventure. Stella’s father sent her on this mission, and the group’s central arc involves returning the hatched dinosaur to its mother before they can go back to modern times. The narrative balances action and peril with educational content, making it both an exciting journey and a crash course in dinosaur science.