Although Burroughs' Martian series grew to a total of eleven volumes, the opening novel, A Princess Of Mars, presents several never explained mysteries. When John Carter returned to Earth after ten years on Mars, he found, at the back of the Arizona cave where his Terrestrial body had lain for those ten years, a mummified old woman leaning over a copper vessel containing green powder above a small charcoal burner, the woman's dead hand still holding a thong connected to a hanging row of human skeletons that rustled like dead leaves when Carter touched the thong.
These discoveries explain sounds heard, an odor smelled and a vapor noticed before Carter's departure as well as the fear of his Apache pursuers who had looked into the cave while he was paralyzed but had then fled in terror. But who was the woman? Why the skeletons? What was the powder? Why did the vapor paralyze Carter? How was he able to leave his body not as a wraith but in another equally physical body? How was that second body drawn across space to Mars, the planet with which Carter as a soldier had always felt an affinity and which turns out to be inhabited by several warlike races? Why does Carter not remember any childhood? How can he be regarded as related to Burroughs if his own antecedents are unknown?
Stirling compounds the mystery by informing us that the hero of his Martian novel had found an Arizona cave with exactly the same macabre contents even though the Mars to which he has traveled by spaceship is not ERB's Barsoom. Will Stirling explain this further or is it just included as an ERBian allusion? Philip Jose Farmer expanded on ERB's works, although mainly Tarzan. If Poul Anderson had written even one sequel to ERB's Martian series, then he would have been equal to the task of tying up all these loose ends and also of placing them in a vaster but rational context.
