The blue men sought refuge in the cavern-world a million years ago, as the surface began to die. Now they believe themselves the only living Martians and it is an article of their faith that the surface is not only devoid of life but permanently uninhabitable. They cannot account for the existence of the red Martians they have taken captive, and thus, with a paranoia long inbred, consider them phantoms and ignore their presence.
In the third novel, Goddess of Mars, flying in pursuit of Zad Tomus, who has again captured and carried off his beloved Xana of Kanator, Jad Tedron discovers a city inhabited by people called Azors, who consider themselves of divine lineage as the descendants of Azor Adz, a divinity they believe to inhabit the moon Cluros, and a female divinity, the spirit of the moon Thuria. They are ruled by a gorgeous woman as their jeddara and goddess, Azara, whom they call Daughter of the Two Moons. She conceives of a violent passion for Jad Tedron and would make him her consort, only to be coldly refused, which, of course, leads to his imprisonment in the pits and a succession of adventures.
The climax of the series, or at least of the trilogy, comes when having disposed of their foes, Jad Tedron and Xana are flying back to Zorad, only to discover that in their absence her father has overthrown the jealous jeddak, becoming jeddak in his place, while Jugundus Jad, Tedron's mighty sire, learning that his son has ventured alone into the stronghold of his hereditary enemies, and becoming alarmed at his prolonged absence, directs his war fleet against the neighboring city. The two hosts are drawn up for battle when Jad and Xana fly into their midst. From the debacle they are saved by the arrival of the Zarkol horde, and it is Zandus Zan who mediates their dispute peacefully—if only to prove that even a coldly emotionless, cruel and pitiless green warrior can be sensible of such weak emotions as gratitude and the repaying of friendship.
If a fourth novel is desired (or more), the next book will be The Wizard of Mars and will concern itself with a great, if deranged, Martian scientist named Ulthan Ptome whose genius has led him to the discovery of two unknown forms of energy, the tenth and the eleventh "rays" of light, even as his madness has goaded him into declaring himself the emperor of all Mars, which he intends to conquer by reducing every city which opposes his regime to powder before the ferocity of his energy weapons.
A fifth novel might concern itself with a race of warrior women who have sworn undying enmity to all males—Amazons of Mars.
As the territory is sufficiently vast and the active characters sufficiently numerous, the series could, if desired, be indefinitely extended by the continuous introduction of new settings and plot-elements.
But, as of now, I am interested in obtaining a three-book contract for A Swordsman of Mars, The Mystery Men of Mars, and Goddess of Mars.