This book tells of a chapter of Theodore Roosevelt's life that was not widely known these days, at least before this book was published. After the failure of his Bull Moose party to carry him to a third term as president, T.R. went looking for adventure (probably in an effort to ward off depression). One thing led to another until he very nearly got himself, his son and others killed in the heart of the Amazon River basin.
The dangers of the Amazon rain forest are so thoroughly described in this book that I'm convinced that the reader is more aware of the danger and trouble TR's party was in than the actual participants. Eventually their predicament is so bad that the reader can't see how they can possibly survive. Readers familiar with history will know that it's not yet time for TR to die. Nevertheless, the mystery finally presented by this book is, how in the world are they going to get out this fix alive?
The real hero of this book, in my opinion, is Cândido Rondon the Brazilian who was the real leader of the group. Roosevelt was more famous, but Rondon was the one who made it happen. He was and continued to be known for his lifelong support of the Brazilian indigenous populations. He believed it important not to kill the native peoples. It was an attitude not widely shared then in Brazil, and thus he was ahead of his time with his enlightened beliefs.
One indication of the difficulties experienced by the expedition was that TR lost a quarter of his body weight (220 lbs to 165 lbs) in a two month time span. He was only 5'-8" tall, so 165 lbs sounds like a good weight to me. But physically he ended up in a very weak condition and close to death due to an infection (antibiotics didn't exist yet).
I found Theodore Roosevelt's own version of the expedition at the following web address. The on-line text is from the book Through the Brazilian Wilderness by Roosevelt published in 1914.