John Carter, a veteran of the American Civil War is prospecting for gold when he and his partner encounter Apaches. He escapes them by entering a sacred cave but immediately succumbs to a strange drowsiness. When he wakes up, he’s on Mars, a dying world known to the locals as Barsoom. There, he is a kind of a Superman in reverse, with super strength and super agility, able to leap a thoat (10 feet high green horse) in a single bound, etc. He encounters a tribe of fearsome six armed green humanoids led by Tars Tarkas. They capture a Red Martian princess, Dejah Thoris, whom John Carter spends much of the novel trying to protect.
Mars is a dying world where, surprisingly, the megafauna are the last to go. The Green Martians feel alien, the Red Martians less so. It’s a world where everyone is constantly at war but the survival of all life on the planet hinges on two guys running a single atmosphere plant. It’s morally uncomplicated world or rather John Carter sees it as such. All in all, it’s best enjoyed by following his example and adopting the attitude of when on Mars. The most important lesson from it is don’t mess with his princess!