Nat's mother and father have died, and he is being brought up by an aunt and uncle, the latter being his mother's brother. His aunt does not care at all for boys, and in particular makes sniping remarks at Nat the whole time. But Nat's uncle is very fond of him, and they are great friends. But enter the aunt's brother, a famous naturalist, back from some trip in South America. Nat, who has already shown great interest in collecting specimens from nature, is enthralled, helps him to stuff and catalogue his specimens, and eventually persuades him to take him (Nat) with him on his next trip.