Nomad

The novel concerns Guy Maynard, of Earth, who is rescued from his Martian captors by Thomakein of the planet Eterne, an invisible wandering planet. After spending time on Eterne, Maynard returns to Earth where he uses the knowledge he gained to launch an invasion against the newly discovered planet Mephisto. He returns to Earth a hero, but is later court martialed and driven from the Galactic Patrol. He seeks refuge on Eterne by impersonating their ruler. When he is discovered, he flees to Mephisto and there raises an army enabling him to conquer the Solar system becoming its emperor.