In this, the fourth book chronicling the adventures of Bomba the Jungle Boy as he searches the Amazonian jungles for the truth to his mystery shrouded background, he once again confronts the dreaded headhunters from the Giant Cataract. This is the fourth time they've tasted defeat at Bomba's hands. But they do succeed in burning down the hut of Bomba's close friend, Pipina the squaw, who he rescues, but Cody Carson and Sobrinini wander off and there whereabouts remain unknown throughout this book.
With a heavy heart, Bomba after an intensive search for the pair, leaves Pipina with the Anaru and treks to Jaguar Island, following up on the slim clue given him by Sobrinini when she ruled the Pante on the Island of Snakes. Curiously, the trail takes him to areas Bomba had never explored but then ends up near the Giant Cataract and the Island of Snakes, only further up the same great river they are both on.
En route to Jaguar Island, Bomba is saved from a Puma attack by a nearby cave and Pololu saves him from a pair of Jaguars. Other attacks survived are from caimans and poisonous snakes.
Once he arrives on the island, Bomba is treated as a reluctant guest, in Japazy's house. The half-breed ruler is away in the Abandoned City at this time. As usual, destruction seems to follow the Jungle Boy and Jaguar Island sinks due to the fury of (another) volcano and so another land joins with the village of the headhunters at the Giant Cataract, Jojasta's temple at the Moving Mountain and Sobrinini being cast out of Snake Island.
One wonders why it is that everywhere Bomba wants to go is shrouded in mystery as lands of terror, yet the rulers of these lands couldn't have resided there for more than fourteen years? And do we ever really learn Jojasta's role in all of this? At book's end, Bomba starts out for the Abandoned City as Jaguar Island slides beneath the waves of the great river.