East Africa, early 1950s. The peaceful Galana tribe are forced to relocate from their rural land because of soil erosion. Despite the views of their leader, Ushingo, and the warnings of game warden Bob Payton, the tribe vote to move to Mombasa. The young men of the tribe are soon preyed on by Mombasa's city criminals, who want to use their hunting skills to poach ivory.

Months later, Bob finds a group of ivory poachers. Their ring leader escapes but Bob catches Ushingo's sons - Ambrose and Bethlehem - among the group. He returns them to Ushingo, who admits that members of his tribe are involved in an ivory smuggling ring. Bob goes to the district commissioner, who suggests they investigate the smuggling ring so Bob travels to Zanzibar with his wife Mary, son Tim and aide M'Kwongwi.

In Zanzibar City, they visit Khingoni's shop, which is trading in illicit ivory. There they encounter a rich Dhow captain, who disappears when he spots . Tim befriends a boy, Juma, who confirms that the Dhow captain is smuggling ivory and leads Bob to his Dhow. Bob and M'Kwongwi attempt to board it but are capsized when the Dhow sail into their tiny boat. Recuperating at home, Bob agrees to Mary's suggestion that he hand the investigation to the police.

M'Kwongwi is arrested for drunken behaviour and, in prison, meets one of the smugglers, who gives him a new lead. After his release, M'Kwongwi goes to work for the smuggler and, with Bob's help, exposes his smuggled ivory. However, once in court, it becomes clear that the smuggler is protecting the leader of the smuggling operation. Bob protests to the lawyer, Dhofar, who dismisses him as a hypocritical colonialist.

Defeated, Bob is criticised as a 'government man' by the Galana. But Ushingo is desperate for his people, so he and Bob follow the Galana tribesmen, who, they know, have become ivory smugglers. They aim to trace the poachers to the unidentified leader of the smuggling operation, but Bob is attacked by a leopard. The attack disturbs the camp and the Galana poachers are murdered by their camp leader.

Mary tries to discover Bob's whereabouts from Ambrose and Bethlehem, who, after threats from M'Kwongwi, agree to help her. They follow Bob and Ushingo's tracks until they spot Bob's bloodied jacket and the dead Galana being eaten by vultures. Ushingo and Bob have the trail of the smuggling ring, but are capsized by a hippo. They return to the camp and are reunited with Mary, M'Kwongwi and Ushingo's sons. Mary demands that the Mombasa police are alerted, but Ushingo wants to regain the Galana pride and sets off to stop the smugglers himself. He is soon joined by the others and they pick up the trail.

Dhofar, now unmasked as the leader of the ivory smuggling ring, suspects that Bob and Ushingo are onto him. He decides to escape the area and accompanies the next batch of smuggled ivory onto the Dhow. Ushingo sees the moored Dhow and goes after it on his own. The Dhow mows him down and he is fatally shot, but the Galana poachers abandon their criminal leaders and join Bob.

Having collected Dhofar, the Dhow seems to get away. But Bob is able to catch up with it downriver, at a point where the river loops back. In the dead of night, Bob and the Galana ambush the Dhow. Ushingo's murderer is killed, the Dhow captain is overpowered and Dhofar is caught. The poachers are arrested and Ushingo's son, Bethlehem, becomes the new Galana chief, promising to look after his tribe.