A small private naturalist's expedition is about to take place up one of the Paraguay rivers. The eponymous hero, Rob Harlow, is a teenager. They are going to be rowed up the river, and the larger vessel that had brought then there, with its Italian captain, is to wait for them. The captain's son, Giovanni, is very keen to come with them, and his father thinks it would be a very good idea. The other adults on the trip are not so happy about the responsibility, but eventually he is allowed to come. He is about the same age as our hero, Rob. There ensue the usual desperate situations we always get from this author. Serpents; people getting lost and eventually found, having losttheir reason; attacks by Indians; insects; pumas; jaguars; and various other problems with animals. There are even quarrels between the boys, arising from a silly misunderstanding. According to Wikipedia: "George Manville Fenn (January 3, 1831, Pimlico - August 26, 1909, Isleworth) was a British writer. He worked as a teacher in Lincolnshire, until he became printer, editor and publisher of various magazines. He had eight children with his wife Susanna Leake, whom he had married in 1855. Most of his work consists of adventure stories for young readers, featuring Explorers, Smugglers, young Adventurers and Seamen. His adult novels offer critical social commentary on Victorian England, especially reconsidering economic questions."