"Dhrusil-matkhashi is a wasteland. The soil is sterile. Why do you suppose we stay on this continent?" Marta, a graduate student researching indigenous life on isolationist Dray's Planet, discovers an animal that can't be indigenous, but which can't have come from anywhere else. The puzzle convinces the Children of the Second Revelation to bring two Unbelievers into their closed society. As the rival offworld scientists trek into the harsh desert...