The book is writen in portuguese, which is the language spoken in Brazil, not spanish. The author has been an adventurer and newsman who explored brazilian hinterland in the years 1930-1960, and wrote many books about his travels and brazilian indians, this one, of 1963, being his last. Biu Marrandu means "the lords of rain" in karajá (tribe of the states of Goiás and Tocantins) tongue, an alusion to the indian god Kananshiwa, creator of the sun, water, wind and rain. The book tells the story of the first expedition to the Uabé river, that runs south-north across Bananal Island, in Araguaia river, word's greatest river island. Today the place is a national park, surrounded of huge soybean plantations and cattle ranchs. The karajás, about 1,000 people, live in a reservation, criss-cross the Araguaia ("river of the mackaw") on motorized aluminum boats, are conected to internet and use cell phones.