The Gods of Mars

First published in 1913 as a five-part serial in All-Story, and later as a novel in 1918, The Gods of Mars is the second book in Burroughs' Barsoom series. 

The Gods of Mars begins with John Carter's arrival back on Barsoom (Mars) after a ten-year separation from his wife Dejah Thoris, his unborn child, and the Red Martian people of the nation of Helium, whom he has adopted as his own. Unfortunately, Carter materializes in the one place on Barsoom from which nobody is allowed to depart: the Valley Dor, which is the Barsoomian afterlife.