Tommy Tomorrow arrives with other rookies at the Planeteer Academy, known as the "West Point of the Solar System". He meets other cadets, such as Lon Vurian of Venus and Lo-Duey of Mars. Someone repeatedly sabotages Tommy, until none of the other cadets trust him. At the end of their training, Tommy Tomorrow and Lon Vurian, the top two students, are chosen to lead two teams in competition to locate the Stone of Gazda which has been hidden on a distant asteroid. The cadets learn too late that Lo-Duey was actually Chardu of Mercury, who has stolen and escaped with the all-powerful Stone.; Tommy Tomorrow and Lon Vurian join together and follow after Chardu. Tommy explains to Lon that when solar rays pass through the Stone of Gazda, they form a wall of energy that can't be penetrated by any weapon. The two cadets succeed in stopping Chardu and regaining possession of the Stone. They are both awarded the Academy Medal of Valor, and graduate with the rank of Lieutenant.