On August 12, 1935, Osa and Martin left the U.S. for their last adventure together, a return to North Borneo. Traveling east by ship they brought only one of their famous amphibian planes. Arriving in Belawan, Sumatra, they reassembled the single engine “Spirit of Africa” and flew on to Sandakan, Borneo, making several stops along the way. The final leg of the journey involved the first flight over a range of mountains deemed dangerous and impenetrable at the time.
From a small base camp near the town of Abai on the Kinabatangan river they traveled by river and air throughout North Borneo recording the customs and rituals of the Tenggara, Murut, Bajou, and Dunsun peoples. The Johnsons also took photos and filmed numerous primates indigenous to Borneo, including the first pictures of the proboscis monkey in the wild.

The daily rains, constant humidity and insects made filming difficult, as it had been 15 years earlier, but the experience gained since then resulted in their finest motion picture yet. They left Borneo in September of 1936 with 3,000 photos and more than 150,000 feet of film.