Tarzan is marked for murder when he clashes with a corrupt government official and his female co-conspirator. The pair are using the natives' beliefs in a monster to drive them away from a rich mineral deposit.

After a guide for an archaeological expedition is killed, Tarzan decides to accompany the group in their quest to enter the forbidden "City Of Death", not only to protect them, but also to find out why a plant specialist and an ambitious colonel are also so interested in the place.

After uncovering the mythical Blue Stone of Baskar, Colonel Tatakombi takes advantage of the legend associated with it to declare himself the leader/god of the surrounding tribes, in the hope of later taking control of the country. Tarzan is determined to expose and stop him.

Tarzan comes across a party of religious pilgrims who are being led by Rosanna McCloud to their "Promised Land". To not shatter their dreams, Mrs. McCloud does not inform her followers that her husband, whom they regard as their Prophet, has just been killed, and she is unaware that the government trader who sold the group the land from a reclusive tribe had his own motives for doing so and never intended for the group to reach it. When Rosanna finally tells her group about the death of their leader, she and Tarzan also find that their money has been stolen.

Rosanna McCloud and her pilgrims are determined to continue in their trek toward their Promised Land, even after one of their people is killed. Now they are armed and determined to fight off the tribe that lives in the land. Tarzan, meanwhile, learns that the chief of the tribe was tricked into selling the land by the trader Whitehead, whom he hopes to expose before more blood is shed.