At the end of World War II Helga, a widow, marries her brother-in-law, a doctor. Together with her two sons Erich and Zeppi, they fly to a distant jungle outpost where Klaus is to be the new medical officer. En route their plane flies into a fierce tropical storm and crashes into a river in a remote region of Amazonas. They are rescued by the Yayomi, a tribe of Stone-Age Indians, and welcomed into their way of life, having been mistaken for land-bound incarnations of freshwater dolphins. At first all goes well, but Erich slowly and painfully begins to realise that Klaus is not the noble figure he thought he was. And that's when things go wrong ...