The mysterious disappearance of Jim Wheatley (Charles Gray), while exploring a cave near a Mexican village, brings his sister, Gina (Mala Powers), and her husband, Dan Matthews (John Howard), to the territory to search for him. Embittered, crippled Pete Morgan (Paul Richards), insists on going along and reminds Dan that his condition is Dan's fault since it happened in an accident in which Pete saved Dan's life. Plus, Gina was Pete's sweetheart before the accident. Did we mention embittered? The party hears about an old Indian legend concerning the Cave of the Dead where human sacrifices were made to the Gods. Dr. Ramsey (Gerald Milton), married to a native girl, Concha (May Wynn), claims no knowledge of the cave, but he is here because the climate is ideal for rapid fungus growth for his work on cultivating fungus for antibiotics. You don't have to be from France to know that if the climate is good for fungus growth, a cave is even better but it takes Dan and Pete a while to get around to that.