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 lost their reason; …
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