The Gods of Mars (version 2) - Edgar Rice Burroughs

In this second volume of the Barsoom series, John Carter returns to Mars to learn that his heroic effort to salvage the atmosphere plant saved the planet's inhabitants, but he finds himself in the land of the dead. Luck restores his friends and even his son to him, and with them he escapes his imprisonment after unmasking (but not deposing) the cruel "goddess" Issus. He finds the Martians unready, however, to fling off their ancient religion and face the frightful truth of what "eternal peace" awaits those who make the voluntary pilgrimage to the Valley Dor. Worse, his wife's father and grandfather have failed to return from searching for him, and his wife in despair has taken the fatal pilgrimage down the River Iss. In their absence his worst enemy has seized power, and since John Carter has committed the unforgivable crime of returning from the land of the dead, all agree—for different reasons and with different intentions—that he must return to it. (Summary by T. A. Copeland)