In a hidden kingdom where dinosaurs roam freely, Carthus is trapped.

The fourteen-year-old orphan guards a stegosaurus herd for his uncaring uncle and dreams of training as a dinosaur rider at the ancient school of Koganri. The problem is, he's a commoner, so his only hope is to pass an impossibly hard entrance exam. After countless hours of study, Carthus earns the kingdom's only passing grade.

However, elite schoolmasters group him with the misfits and foreigners in their plot to rid Koganri of students they deem unworthy. Carthus must win a series of dinosaur-riding competitions, or his chances of staying at the school are nil. But he can't win the Maybranch alone—it's a team competition. To keep his dream alive, Carthus must help his teammates get along so they can joust on gallos, fly on pterodactyls, and give commands to a surly t-rex. The fate of their future depends on it, even more than they know.