The Gods of Mars "A Science-Fiction Novel"

The Gods of Mars is a science fantasy novel by American writer Edgar Rice Burroughs and the second of Burroughs' Barsoom series. It features the characters of John Carter and Carter's wife Dejah Thoris. It was first published in The All-Story as a five-part serial in the issues for January-May 1913. It was later published as a complete novel by A. C. McClurg in September, 1918 and in many editions subsequently.
As usual for him, Burroughs begins with a frame story that explains how he (Burroughs) came into possession of the text. At the end of the first book, A Princess of Mars, John Carter was unwillingly transported back to Earth. 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. Unfortunately, Carter materializes in the one place on Barsoom from which nobody is allowed to depart: the Valley Dor, which is the Barsoomian afterlife.
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. Most arrivals are killed by the beasts who dwell here, and the survivors enslaved or eaten by Therns.
Carter and Tars Tarkas rescue Thuvia, a slave girl, and attempt to escape, capitalizes on the confusion caused by an attack by the Black Pirates of Barsoom upon the Therns. During the attack, Tars Tarkas and Thuvia hijack a Black Pirate flier, while Carter fights his way aboard another, killing all but one of the Pirates, and rescuing a captive Thern princess. From the captured Pirate Xodar, Carter learns that the Black Pirates, called the "First Born", also think of themselves as gods, and accordingly prey upon the Therns; and additionally identifies the captive Thern as Phaidor, daughter of the "Holy Hekkador" (high priest) of 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.