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.