Keith Brandon enlists Hal Scott, David Richardson, Dr. Loren, Tex Morgan and Forrester in an expedition to locate a lost treasure buried beneath an ancient Incan city. Led by Indian guides Gracco and Mala, the men penetrate the "green hell" of the Amazon jungle until they find the subterranean passage leading to the hidden temple. However, as Richardson emerges from the tunnel, he is wounded by poisoned arrows shot by hostile Indians, and Brandon sends Bracco and his men back to civilization for ammunition, provisions and serum for the dying Richardson. The natives return with Richardson's wife Stephanie, who learns that her husband has died. Soon after, the natives desert, and Stephanie is stranded in the jungle camp, where her presence fosters jealousy between Forrester and Brandon and dissension among the others. Brandon, who is in love with Stephanie, plans to escort her out of the jungle, but on the eve of their departure, Stephanie learns that her late husband had another wife, and consequently feels betrayed by all men. Their departure is delayed when a raging storm strikes, and while trying to save the excavation of the lost temple, the men discover a buried crypt laden with gold and a curse of death on whomever disturbs the treasure. The curse appears to be coming true when hostile savages lay seige to the camp, and after the killings of Graham and Forrester, death for the remainder of the group appears imminent. As Stephanie pledges her love for Brandon, Mala and his tribe appear to slay the attackers and save the expedition.