The story proper begins with his arrival back on Barsoom (Mars) after a ten-year separation with Dejah Thoris, their unborn child, and the Red Martian people of the nation of Helium, whom he has adopted as his own.

After John Carter's arrival, a boat of Green Martians on the River Iss are ambushed by the previously unknown Plant Men.

The lone survivor is his friend Tars Tarkas, the Jeddak of Thark, who has taken the pilgrimage to the Valley Dor to find Carter.

Having saved their own lives, Carter and Tars Tarkas discover that the Therns, a white-skinned race of self-proclaimed gods, have for eons deceived the Barsoomians elsewhere with the lie that the pilgrimage to the Valley Dor is a journey to paradise.

Carter and Tars Tarkas rescue Thuvia, a slave girl, and attempt to escape, capitalizing on the confusion caused by an attack by the Black Pirates of Barsoom upon the Therns.

When their flier is recaptured by the First Born and taken to their underground realm of Omean, Carter is taken before Issus, the self-proclaimed goddess of Barsoom, who dictates the Therns through secret communications which they mistake for divine revelation.

Upon later abandoning their aircraft, they encounter Thuvia, who describes the capture of Tars Tarkas by the green warriors of Warhoon (a clan rival to his own).

After seeing that the warships of the Therns and the First Born fought whenever they encountered each other, he ordered his Heliumetic ships to disengage and withdraw to the southwest of the battle.

Carter, Carthoris, and Kantos Kan would lead the rest of the fleet (500 ships) to Omean, to attack through the pits under the temple.

During the march, the water had risen to such a level that Carter was forced to call a portion of the troops to enter a diverging tunnel.

The men in the chamber also witnessed the charge of the Green warriors, which broke the thin black line defending the garden.

Issus went insane, and during her mad rant, she told Carter that Dejah Thoris, Thuvia, and Phaidor are imprisoned in the Temple of the Sun, each of whose rooms opens only once per year.

Immediately before their room closes, Phaidor attempts to kill Dejah Thoris, and her success or failure are left unknown.

The Valley of Dor, the River Iss and the Sea of Korus were all key locations in the Martian conception of heaven or the afterlife, which Burroughs had introduced in A Princess of Mars.

John Carter "visits" Burroughs 12 years after the events of A Princess of Mars, claims to have mastered the secret of interplanetary travel, and states that it will be the last time that he makes such a journey from his adopted home.

[8] Planetary romances mostly take place on the surface of an alien world and frequently include sword fighting, monsters, supernatural elements such as telepathic abilities (as opposed to magic), and civilizations similar to Earth in pre-technological eras, particularly with the inclusion of kingdoms, empires or religious societies.

Spacecraft may appear, but are not central to the story, which makes these tales distinct from Space Opera in which spaceships are usually a key focus of the narrative.

[7] Burroughs's vision of Mars was loosely inspired by astronomical speculation of the time, especially that of Percival Lowell, who saw the planet as a formerly-Earth-like world that was now becoming less hospitable to life because of its advanced age and whose inhabitants had built canals to bring water from the polar caps to irrigate the remaining arable land.

[9] The Valley of Dor, with the ring of cliffs around it and Sea of Korus within it, is placed in a mile-deep crater at Mars' south pole.

However, Burroughs makes a mistake in that he has the sun rise in the east and set in the west, like elsewhere in the planet, and the moons are visible from the Valley.

John Carter spent his first ten years on Mars without knowing of the existence of the other races, aside from ancient paintings and frescoes that depicted White Martians.

The Gods of Mars introduces two new races; the White-Skinned Therns and the Black-Skinned First Born, both of which are strongly connected to the Martian religion that John Carter exposed in the novel.

They raid the White Martian Therns; carry off girls as slaves; and have a massive aerial navy, which John Carter defeats.

Upon reaching 1,000 years of age, almost all Martians undertake a pilgrimage along the River Iss and expect to find a valley of paradise but find in fact a deathtrap, which is populated by ferocious creatures and overseen by a race of cruel cannibal priests, known as Therns, who perpetuate the Martian religion through a network of spies across the planet.

[17] More deceitful priests in a theocratic nation appear in The Master Mind of Mars in which they manipulate a temple idol to control followers.

[27] However, the film's poor box office performance put plans for sequels on hold,[28] Eventually they were cancelled and in 2014 Disney allowed the rights to the novels to revert to Burroughs' estate.

[29] In 2022, 10 years after the film's release, director and cowriter Andrew Stanton shared details of how the sequel would have begun with TheWrap.