The narrative begins in the magnificent palace of Helium, where Princess Tara, granddaughter of Tardos Mors and daughter of John Carter, lives a life of effortless elegance. During an exceptionally violent Martian gale, Tara impulsively takes her light flier into the clouds to experience the tempest firsthand. Overpowered by the storm, her craft is blown across thousands of haads into the remote, desolate valley of Bantoom, a legendary region inhabited by the kaldanes—gigantic, disembodied brains that animate mindless, headless bodies called rykors. Tara is captured by these repulsive creatures and brought before Luud, their king, who intends to fatten her for consumption. Despite her peril, she maintains the indomitable spirit of her famous lineage, continually seeking a means of escape with the help of Ghek, a dissident kaldane whose brief exposure to Tara's humanity and music has awakened strange, uncharacteristic emotions within him.
Simultaneously, Gahan, the Jed of Gathol, who had previously declared his love for Tara at Helium, sets out in a desperate search when he discovers her disappearance. During the pursuit, Gahan's airship is shattered, and he is cast down into the wilderness. After weeks of perilous wandering, he reaches the edge of Bantoom just as Tara is struggling to regain her freedom. Gahan infiltrates the citadel of the kaldanes, witnessing firsthand the grotesque horror of the subterranean burrows where rykors serve as mere vehicles for the supreme brain.
Following a daring infiltration and a fierce clash with the defenders of Bantoom, Gahan, Tara, and the renegade kaldane Ghek escape into the trackless Martian wastes aboard the repaired flier. Their journey leads them to the ancient, isolated city of Manator, whose inhabitants adhere rigidly to ancient, unyielding laws and maintain an eerie silence behind their stone walls. Upon arrival, they are immediately captured by the savage warriors of the Manatorian jeddak, O-Tar. Separated and thrust into the dark palace pits, Tara faces a grim fate as a prize in the brutal arena games of jetan, where living men fight to the death. Gahan, operating in disguise as a simple panthan, maneuvers through the political intrigues of the city, aided unexpectedly by A-Kor, the dissident son of the jeddak.
The climax builds as political tension boils over between O-Tar and U-Thor, the noble Jed of Manatos, who commands a massive army outside the city walls. Inside the palace, Ghek utilizes his terrifying mental powers to paralyze the jeddak, granting Tara and Gahan a narrow window to flee into the subterranean mazes. Pursued through the dark, ancient corridors and encountering bizarre inhabitants of the underworld, the protagonists fight desperately to reach the city gates. The story culminates in a dramatic confrontation that tests the resilience of the human spirit against both physical perils and the chilling doctrine of absolute reason.
