Captain Lanthan and his best friend 2nd pilot Cheris are forced to make a crash-landing on the surface of Protion after their cargo spaceship receives unrecoverable damage from asteroids. Here begins a journey full of danger and surprise. Their initial goal is quite clear: they must escape the hostile alien world where they are no more than doomed prisoners. But soon afterwards they start their wandering, Lanthan and Cheris find out that Protion possesses the only deposit of priceless mineral tactonium in the whole Galaxy. The extraction of this mineral is under the severe control of the mighty Empire. Protion is completely separate from the outer world, and the only spaceship suitable for leaving the planet is owned by the Empire. Three main races inhabiting the planet work in mines as imperial slaves. The duty of our heroes is now to unite all the peoples of Protion and raise a rebellion to bring deserved freedom to the oppressed. Standing at the head of the furious struggle, Lanthan and Cheris will learn more about the mysterious fourth race of noble Nomads that are secretly confronting the Empire, and through all the hardships reach the unpredictable final of this story.