An Earthman who can traverse the void returns to Mars to rescue his missing Martian wife and determine the fate of their son. His quest leads through Barsoom's dying landscapes and diverse societies, from strange plant-like creatures and green warriors to fanatical priest-castes and lush city-states. He survives prison, treacherous sea and air combats, pirate raids, and encounters with a cult claiming control over life and death, while allies reveal hidden loyalties and losses. The narrative alternates perilous action with revelations about Martian religion, politics, and technology, producing a tale of rescue, sacrifice, and uncertain triumph amid a collapsing world.