After a bitter defeat in the U.S. presidential campaign, Roosevelt sets out in search of his lost youth in the Brazilian Rainforest alongside his long-time friend Farrel Nash and his son Kermit, with the objective of exploring the last uncharted river in the country: the River of Doubt, in Rondonia. 

On a journey fraught with deadly dangers, the former president counts on the support of indigenous expert Marshal Rondon, then responsible for connecting the most remote regions of the country. On this journey, the two men from different backgrounds will have to test their physical and moral limits, as well as learn to deal with their conflicting personalities in order to survive.