Thousands of years in the future, the protective layers of the atmosphere have slowly been eroded due to increasing greenhouse gases. Due to this, the Earth is no longer as protected from the sun's harsh heat and radiation and much of Earth's landscape has become desert. To survive this, certain humans have adapted features that allow themselves to live in the overwhelming heat including large ears that more efficiently expel heat, long eyelashes to protect from sand, and dark pigment around the eyes to shield from glare.
To find water, members of the village rappel down into huge, sinkhole like caves where water pools in trenches left over from the dried up oceans. The main character is one of these well jumpers, who ends up accidentally falling into a cave and is saved by a member of the subspecies of humans that adapted to live in caves. Eyeless, almost translucent from lack of pigment, and communicating only through sonar, the cave humans were previously unknown to the desert people, or so the main character thought.