In April of 1925, a decorated British military surveyor named Percy Fawcett walked into the Mato Grosso region of Brazil with his twenty-two-year-old son Jack and Jack's closest friend Raleigh Rimell. His last confirmed letter arrived from a camp called Dead Horse Camp in late May. After that, a Kalapalo Indigenous community reported watching the smoke from their campfire rise above the treeline for five days. On the sixth day, the smoke stopped. Percy Fawcett, his son, and Raleigh Rimell were never seen again. But Fawcett's disappearance is not the most extraordinary part of his story. For twenty years before he vanished, Fawcett had been building a meticulous, evidence-based case for the existence of an ancient, large-scale civilization in the Amazon basin — a civilization he called "Z." He had physical evidence: pottery fragments in regions decla ...