The novel revolves around the mysterious life and times of John Carter, a Confederate veteran of the American Civil War. Shortly after the end of the war, he decides to become a prospector in Arizona and strikes it rich, locating a particularly prolific vein of gold. The gold however is located within Native American (Apache) territory and they do not take kindly to John’s intrusion upon their land. They kill his business partner, James K. Powell, while he is on his way to town to replenish their equipment and supplies and now they plan to finish off Carter as well and give him chase. John Carter flees from his pursuers and escapes them by hiding in one of the sacred caves, and exhausted from running he quickly falls asleep. He wakes up on horror though realizing that despite being fully awake, he is unable to move. He tries desperately to will himself into motion but finds himself having an out-of-body experience, seeing his own naked form looking down upon his still body lying motionless on the cave floor. He panics and leaves the cave in a hurry. Looking up at the night sky, he sees Mars and as he reaches out to the remote planet he is suddenly pulled through the vast distance of space.
Carter is transported, almost instantaneously to the planet Mars via mysterious means. Upon finding himself on Mars he discovers that he now possesses superhuman strength and agility; a result of lower gravity of and lower atmospheric pressure of Mars, or Barsoom as it is known by its inhabitants. Not too long after his sudden and inexplicable arrival upon Mars when he is discovered by a party of Tharks, the native inhabitants of the planet. The Tharks are green-skinned, six-limbed, and tusked humanoids that live in loose tribal units. They are also belligerent race that value raw, physical strength and martial prowess above all else.
His unnatural Terran strength, his military training, and experience pay off greatly as he manages to defend himself against his would-be captors. Upon seeing his skill with a blade, his amazing strength, and utter fearlessness the Tharks take his as a kindred spirit, earning both the respect and friendship of the Thark Chieftain, Tars Tarkas. He rises to a position of prominence within the tribe in due time, honoring him by giving him a new Barsoomian name, Dotar Sojat, a cognate name formed from the combination of the names of two prominent warriors that he had defeated in single combat.
The Tharks are a society of raiders and they later capture the Princess of the City-State of Helium, the beautiful Dejah Thoris. Dejah belongs to the Red Martian race, a species of Martian more closely resembling human beings save for a deeply tanned, nearly brick-colored skin hue, hence their common name. The red Martians reside in widely spaced grid of independent city-states. They also hold influence over the few remaining canals upon the bone-dry Martian surface where unsurprisingly most of the farming is done.
John Carter frees Dejah Thoris from the Tharks and returns her to her people. Consequently, his rescue of Dejah Thoris results in his involvement in the messy political dealings of both the Red Martians and the Tharks. Eventually, through a combination of raw might, charisma, and sheer bravado he manages to win over both the Red Martians and the Tharks, forming a tenuous peace between the two races. His stay on Barsoom is marked by a number of great escapades: he is imprisoned by the Warhoons, a horde of nearly feral Tharks, but he eventually defeats them. He locates the Atmosphere Factory, a vast terraforming edifice that, as its name suggests, is responsible for producing all the air that the native Barsoomians breathe. His adventures culminate in his epic battle with Helium’s bitter, historic rival, the city-state of Zodanga. He leads a great horde of Tharks against their hated enemy and together they finally defeat them.
His victory over Zodanga catapults him into greatness, eventually becoming himself a Prince of Helium, and marrying Princess Dejah Thoris. Their happy union lasts for nine years, until the tragic, sudden failure of the Atmosphere Plant. It’s failure meant death for all life on Barsoom. Carter sends out an encrypted telepathic message to be allowed entrance along with an mechanic skilled enough to repair the complex machinery of the Atmosphere Plant into the plant’s inner complex. Unfortunately, Carter is overcome by the lack of oxygen and he passes out, only to mysteriously awaken back on Earth--Jasoom--as the Martians called it. A badly confused John Carter is now left to ponder the fate of his kingdom, his subjects, and his beloved princess.
