Two medical doctors climb the rugged South American slopes of a great volcano, reputed to have vapors that can cure some tropical diseases. While being lowered into the volcano, Dr. Cantillo's hand slips and his partner falls into the volcano, emerging as an ashen-cover thing that Cantillo dispatches with a large boulder. The Heap, watching the whole thing, follows Cantillo, who discovers a use for the strange vapors, who uses the knowledge to bilk people out of their money.