The Gods of Mars recap

After ten years on Earth, John Carter returns to Barsoom in the Valley Dor, where he reunites with Tars Tarkas and learns that the planet's promised pilgrimage ends in predation and captivity. They rescue Thuvia of Ptarth, confront the white therns who maintain the religious deception, and are drawn into the hidden realm of the First Born beneath the valley. Carter meets the warrior Xodar and exposes the supposedly divine Issus as a mortal ruler. He also finds Dejah Thoris alive but imprisoned. After escaping, Carter returns to Helium, meets his grown son Carthoris, survives prosecution for returning from the Valley Dor, and gathers an alliance to free the captives. The attack destroys Issus's authority, but Matai Shang seals Dejah, Thuvia, and Phaidor inside the rotating Temple of the Sun for a full Barsoomian year. As their chamber closes, Carter sees the jealous Phaidor raise a knife against Dejah and cannot reach her.

Previously: John Carter was transported from an Arizona cave to Barsoom, where the planet's lower gravity gave him unusual strength. Captured by green Martians, he befriended Tars Tarkas, Sola, and Woola, and fell in love with Dejah Thoris, princess of Helium. He united Thark warriors with Helium, stopped Dejah's forced marriage to the prince of Zodanga, and helped defeat that city. Tars Tarkas became jeddak of the Tharks, while Carter married Dejah. Nine years later, with Dejah expecting their child, the atmosphere plant sustaining Barsoom failed. Carter entered the sealed facility and restarted its machinery, but immediately woke in his body on Earth. Ten years passed there without any sign from Barsoom, so he did not know whether the planet, Dejah, or their child had survived.

Carter is finally transported back to Barsoom but arrives in the Valley Dor, the destination of the voluntary pilgrimage that Barsoomians are taught to regard as sacred and final. The valley is instead filled with plant men and great white apes that attack new arrivals. Carter unexpectedly finds Tars Tarkas and fights beside him. In the surrounding caverns they learn that white-skinned therns exploit the pilgrims and preserve the religion that sends victims into the valley. They meet Thuvia, a captive princess of Ptarth who understands the valley's creatures and can command its banths. The three seek a path out while the therns try to prevent them from carrying what they have learned back to the wider world.

Carter, Tars Tarkas, and Thuvia escape the immediate dangers of the Valley Dor but enter the conflict between the therns and the First Born, black Martian raiders who travel through the hidden Sea of Omean. Carter fights Xodar, a senior First Born warrior, and is carried into the underground realm ruled by Issus. Phaidor, daughter of the thern leader Matai Shang, is among the prisoners drawn into the same struggle. Her religious certainty and interest in Carter make her a volatile companion. The layers of authority are now clearer: ordinary Barsoomians revere a pilgrimage controlled by the therns, while the therns themselves fear the First Born, who in turn worship Issus.

In Issus's court, Carter discovers that the supposed goddess is a mortal ruler who maintains power through secrecy, ritual, and the unquestioning loyalty of the First Born. He sees Dejah alive among the captives, along with Thuvia and Phaidor, but cannot free them immediately. Issus sends Carter and Xodar to the prison island of Shador. When Xodar learns that his ruler is willing to discard even faithful servants, his certainty in her divinity breaks, and he joins Carter. They organize an escape and begin turning the First Born's own routes and machines against Issus's regime. Carter's purpose is now both personal and political: reach Dejah and expose the linked systems that have kept the Valley Dor and Omean beyond challenge.

Carter and Xodar escape the First Born and eventually reach Helium, where Carter expects help. Instead, his return from the Valley Dor violates a deeply rooted religious prohibition, and Zat Arras, the Zodangan jed exercising authority in the city, orders him arrested. Carter is reunited with loyal allies including Kantos Kan but finds that Dejah remains a prisoner and that public belief makes an open rescue difficult. He also learns that the child Dejah was expecting when he vanished survived: Carthoris is now a grown prince of Helium. Father and son meet for the first time while Carter faces judgment for bringing forbidden knowledge back from the pilgrimage.

Carter is condemned under the old religious law, but Carthoris, Kantos Kan, and other loyalists help him escape. Evidence of the deception in the Valley Dor begins to weaken the authority behind the sentence. With support from Helium, Ptarth, the Tharks, and Xodar's allies, Carter gathers a fleet for a direct assault on the therns and the First Born. Zat Arras attempts to obstruct and then exploit the expedition, but Carter retains the loyalty of the forces committed to freeing the prisoners. The coalition reaches the hidden domains around Omean and begins the battle to overthrow Issus's court and recover Dejah, Thuvia, and Phaidor.

Carter's allied forces break into the hidden strongholds. Issus is publicly exposed as mortal, and the First Born turn against the ruler they had worshiped; her regime collapses, and Xodar emerges as a leader among his people. Dejah, Thuvia, and Phaidor are sealed in one of the rotating chambers of the Temple of the Sun, each of which opens to the outside only once in a Barsoomian year. Carter remains beside the temple, unable to force an entrance. In the final instant before the chamber moves fully out of view, he sees Phaidor raise a knife toward Dejah. The door closes, leaving Thuvia and Dejah trapped and Dejah facing an immediate attack while Carter can only wait outside.

Carter's coalition attacks the domains of the therns and First Born. Issus is exposed as mortal and loses the obedience on which her rule depends; her regime collapses, while Xodar rises among the freed First Born. Dejah, Thuvia, and Phaidor are sealed inside the Temple of the Sun, whose chambers open to the outside only once during a Barsoomian year. Carter can do nothing but watch the rotating prison from outside. As the doorway carrying the women passes from sight, he sees Phaidor raising a knife toward Dejah. The opening closes before he can intervene, leaving Dejah and Thuvia trapped and Dejah in immediate danger from Phaidor.