Several big game hunters, headed by Major Frederick Brown, scientist and sportsman, travel to Mombasa in Kenya to begin their search for the gorilla. From Mombasa, they travel upriver through mangrove trees that contain oyster beds in their roots. The expedition encounters hippopotami, pythons, crocodiles and small carnivorous fish as well as gnu and giraffes. They hunt rhino, gazelle and elephant. The hunters witness a lion attack and afterward kill several of the animals. The expedition moves into the area around the Congo called French Equatorial Africa, where they encounter the Ubani. The Ubani expand their lips by inserting progressively larger discs into a slit until they are the desired size. Further upriver, they stop at a Kavirondu village. The Kavirondu consider the leopard sacred. The expedition decides to trap a live leopard while they are in the area. The Iturbi forest is inhabited by Pygmy tribes. The Pygmies are extremely knowledgeable about the habits of the gorillas and serve as guides on the expedition. When they arrive in gorilla country, the hunters make their camp beneath Mt. Kilimanjaro. The local tribes believe that the souls of their ancestors inhabit the gorillas. The hunters learn that gorillas build their homes in the trees and that the homes are protected by the male gorillas, who remain at the foot of the tree. The expedition captures a baby gorilla. The next day, the Mambuti try to sacrifice a woman to the gorillas, but the hunters kill a gorilla and his mate and free her.