A scientific expedition of the “Earth Resources Utilization Technology Service” searches for diamonds in Congo. The African tropical forest stretches for hundreds of kilometers—an isolated world alien to humans. Strange circumstances lead to the death of members of the expedition. From now on, Doctor Karen Ross has to find a way to the legendary city of Zinj, lost in the heart of Congo—for two reasons: to locate diamond deposits with unusual properties, and to investigate the causes of the company’s expeditions’ deaths in Africa.
Ross assembles a third team, including two African warriors, Peter Elliot, an expert on gorillas, and… Ami the gorilla, who knows about 600 words in sign language. As soon as the team sets up camp at the Lost City, they are attacked by an unknown gray gorilla variety. Several team members are killed and wounded, others try to repel the attacking gorillas. The desperate situation is resolved by Ami, who “speaks” with the gray gorillas in their native “language.” Will the diamond deposit be found, and how will the situation with the gorillas be resolved—including Ami?