On their travels in British North Borneo, Martin and Osa Johnson depart from Sandakan and proceed up the Kinibatangan River into the heart of unexplored country, traveling in native boats called gobongs. They hunt crocodiles, shoot rapids, visit with natives, examine places frequented by a gang of Malaysian pirates, and observe many animals, including water buffalo, elephants, monkeys, gibbons, apes, an orangutan, bears, and deer. The journey ends with the Johnsons' safe return to Sandakan.