A narration by Dr. Frank Baxter, an English professor at the University of Southern California, explains the premise of the movie and its basis in reality. He briefly discusses the hollow earth theories of John Symmes and Cyrus Teed among others, and says that the movie is a fictionalized representation of these unorthodox theories.
Archaeologists Dr. Roger Bentley and Dr. Jud Bellamin find a race of Sumerian albinos living deep under the Earth. They keep mutant humanoid mole men as their slaves to harvest mushrooms, their primary food source, since mushrooms can grow without sunlight. The Sumerian albinos' ancestors relocated into the subterranean after cataclysmic floods in ancient Mesopotamia. Whenever their population increases, they sacrifice old people to the Eye of Ishtar, which is really natural light coming from the surface. These people have lived underground for so long that they are weakened by bright light which the archaeologists brought in the form of a flashlight. However, there is one girl named Adad who has natural Caucasian skin who is disdained by the others since she has the "mark of darkness." They believe the men are messengers of Ishtar, their goddess.
When one of the archaeologists is killed by a mole person, Elinu, the High Priest, realizes they are not gods. He orders their capture and takes the flashlight to control the Mole People, not knowing it is depleted. The archaeologists are then sent to the Eye just as the Mole People rebel. Adad goes to the Eye only to realize its true nature and that the men had survived. They then leave for the surface. Unfortunately, Adad dies after reaching the surface, when an earthquake causes a column to fall over and crush her.
Who are the archaeologists?
Dr. Roger Bentley and dr. Jud Bellamin