Even so, these travelers were generally quite serious about their own ambitions, as if their efforts to map some irrelevant river put them in the same class as Pizarro or Cortés. The books that resulted from their South American travels were cut from the same dull cloth. In 1913, having failed to win the presidency as the candidate of the Bull Moose Party, an aged and remarkably ill-prepared Theodore Roosevelt set out on a Brazilian expedition. His book, Through the Brazilian Wilderness, explained how he had plumbed the darkest interior, inspired the government to spruce up the Rio da Dúvida with a new name (Rio Roosevelt), and faced down the deadly piranha: “The rabid, furious snaps drive the teeth through flesh and bone. The head with its short muzzle, staring malignant eyes, and gaping, cruelly armed jaws, is the embodiment of evil ferocity; and the actions of the fish exactly match its looks.” (“All one can say,” writes John Ure in Trespassers on the Amazon, “is that his companions did not begrudge him his final fling.”)

Roosevelt was preceded by the flamboyant writer and explorer Henry Savage Landor, who, according to David Grann, roamed the Brazilian interior “dressed as if he were heading off to a luncheon in Piccadilly Circus.” Landor’s own Across Unknown South America combines a bluff and imperious tone with the narrative verve of a shipping manifest. When not describing the scenery in slide-show fashion or endlessly marking the changes in elevation, the author complains of the country’s inadequate accommodations and the “contemptible imbeciles” with whom he was forced to travel. Landor’s men “mutinied and nearly shot him,” writes Grann; any of us would have done the same.

Most relevant to Fleming’s ambitions was G. M. Dyott, an Englishman who, in 1928, led a widely publicized expedition to find the vanished Colonel Fawcett. Man Hunting in the Jungle, his account of the trip, is written from the perspective of someone who very much wants you to know how much he suffered while in transit. Dyott sets the tone with the frontispiece, a ominous photograph of tangled vines captioned, “The Jungle greets you with a Hangman’s Noose.” He takes enormous pleasure in listing the hazards that he faced, noting early on that “some jungle malady may grip your flabby body from within and snuff out life quicker than the wind disposes of a lighted candle.” It is tedious stuff, and the reader occasionally wishes that Dyott’s prediction had come true.

Peter Fleming was not at all this sort of person. But he was greatly amused by those who were. And so he signed onto the expedition as a special correspondent for the Times. After securing a book contract and recruiting a companion—a lanky surveyor and Oxford grad named Roger Pettiward, who would later find fame as a cartoonist under the pseudonym Paul Crum—Fleming left his job at the Spectator (“the act of a madman,” he put it) and headed for Brazil with high spirits and low expectations.

The party sailed in the late spring of 1932, toting shotguns, revolvers, tear-gas bombs, a bull mastiff named Boris, a gramophone, the organizer’s father, the organizer’s father’s chauffeur, and several obsolete maps. At first, finding Fawcett was a secondary goal of the expedition. In fact, most members of Fleming’s party were under the impression that they were on a simple hunting trip. But after docking in Rio, Fleming insisted everyone sign a “gentleman’s agreement” asserting that their primary objective was to locate the missing colonel, to which his fellows uneasily assented. (“We shared a working knowledge of firearms, and a more or less keen interest in the habits of wild animals and birds: but by no stretch of the imagination could ours be considered a scientific expedition,” wrote organizer Robert Churchward in his apologetic account of the journey, Wilderness of Fools.)

Justin Peters is editor-at-large of the Columbia Journalism Review.