Waters of Doubt. DiPaolo, #3

Waters of Doubt, third tale in the DiPaolo trilogy, a novella. Theodore Roosevelt has invited Martino DiPaolo to an exciting vacation in the Brazilian rain forest. The trip nearly proves the last of both men, as well as the rest of the expedition. They have chosen to follow the course of an unmapped river, the River de Duvidas, River of Doubt. But DiPaolo is shown an ancient, secret world. Meanwhile at home, DiPaolo's arch enemy Kwanyin Luk is hatching his own plans.
He has created the greatest confidence game of his career: the di Paolo estate con. He is making millions of dollars and can't be touched. Then he decides to go after DiPaolo himself, with a gun.