Bruce Kellog and his friend Andy are preparing an expedition to Africa to search for the legendary City of the Dead, which Bruce hopes to photograph. His wealthy fiancée, Betty Graham, bored with her life of leisure, tells her father William that they should accompany Bruce and Andy. William is not sure the jungle is an appropriate place for a woman, but the prospect of seeing his brother Jim, who has been a missionary in Africa for the last thirty years, wins him over. In Africa, meanwhile, Father Jim confers with Dr. Hammond, a handsome American who has spent the last five years trying to develop a cure for the deadly "malaka fever." An experimental batch of the serum Dr. Hammond invented has been produced in the United States and is now on its way to Africa, but the doctor fears another epidemic and is not pleased when drums announce the arrival of their American visitors. That night, at a banquet given by the local native tribe, Dr. Hammond reluctantly agrees to give Bruce and Andy maps to the City of the Dead, although he warns them that no one has made it back from there alive. The men set out the next morning, and after Dr. Hammond rescues Betty from a lion, an attraction begins to develop between them. Father Jim then gives Dr. Hammond the bad news that the ship carrying the serum from America has been sunk just off the coast. Meanwhile, after a difficult journey, during which they have to rescue their inept guide, Buck, from a huge boa constrictor, Bruce and Andy finally reach the City of the Dead, and together they explore the exotic ruins and take photographs. Back at the camp, Dr. Hammond is summoned to the nearby Posa Village, where a new case of the fever has been discovered, and Betty insists on going with him. As they leave, they spot members of an enemy tribe approaching the settlement, and when one sneaks into Father Jim's home, he is killed by the priest's pet tiger. At Posa Village, Betty is set upon by lions while tending the fever victim, and Dr. Hammond again comes to her aid. After they return to the camp, Bruce and Andy show up, Buck having been killed after their native bearers deserted them. Bruce has been stricken with the fever, and Dr. Hammond decides to try retrieving the serum from the shipwreck. The undertaking is hazardous and claims the lives of two sailors, but Dr. Hammond plunges into the shark-infested waters himself and swims back with the box of medicine. By the time he returns to the camp, Betty has come down with the fever. Dr. Hammond gives her the serum, and several hours later she revives. They kiss.