John Carter returns to Mars. Rather more briskly and with less introduction.
He lands in a waste and soon finds himself in a fight -- and in a fight next to his old friend Tars Tarkas, who reveals him that this is the end of the hallowed pilgrimage Martians take at the end of their lives, this horror of a land. Pressing on through forces of white apes and plant men, they find themselves in the city of therns who habitually enslave and maltreat -- and eat -- the pilgrims. And if anyone escapes to bring back news, the Martians of the outer lands will execute them for blasphemy.
Not that they are unhindered. They are also raided by the black pirates.
His adventures involve blond wigs, a woman who can tame banths (Martian lions, so to speak), John Carter's being enslaved and receiving a slave while one, being forced to look on the "radiant beauty" of a goddess, meeting a young man and a lot of contrived coincidences before he can tell John Carter who his father is, a trial, two young women who tell him they are in love with him, to be rejected as gently as he can, and their two very different reactions to that, and much more.
Warning: this one ends on a cliff-hanger, and not a tacked on one. It's really one story with Warlord of Mars.