Mortally wounded while serving as an American officer in World War I, Ulysses Paxton is mysteriously transported to Barsoom, where he becomes the assistant of Ras Thavas, a brilliant but morally detached scientist who has perfected the transplantation of brains from old or diseased bodies into younger and healthier ones. Paxton falls in love with Valla Dia, only to learn that her beautiful body has been taken by Xaxa, the ruler of Phundahl, and he joins several companions whose brains and bodies have also been exchanged as they escape the laboratory and cross dangerous Martian cities in search of her stolen form. After surviving intrigue, combat, and pursuit, Paxton forces Ras Thavas to restore Valla Dia to her rightful body, bringing the adventure to a close while the novel explores questions of identity, scientific ethics, social privilege, and religious authority through Burroughs’s characteristic mixture of romance, satire, and planetary adventure.
