Its plot devices are similar to the previous Martian novels, involving the kidnapping of a Martian princess. This time John Carter's son Carthoris is implicated. It does however have some inventive and original ideas, including an autopilot and collision detection device for Martian fliers, and the creation of the Lotharians, a race of ancient martians who have become adept at telepathic projection, able to create imaginary warriors that can kill, and sustain themselves through thought alone.Carthoris is madly in love with Thuvia. This love was foreshadowed at the end of the previous novel. Unfortunately Thuvia is promised to Kulan Tith, Jeddak of Kaol. On Barsoom nothing can break an engagement between a man and woman except death, although the new suitor may not cause that death. Thus it is that Thuvia will have none of him. This situation leaves Carthoris in a predicament.