Archaeologists Dr. Roger Bentley and Dr. Jud Bellamin discover an ancient Sumerian artifact while conducting a dig on a remote mountain. The artifact leads them to explore a network of underground passages, where they stumble upon a lost civilization descended from the Sumerians. This society has remained hidden for thousands of years, worshipping the goddess Ishtar and living in a world devoid of sunlight, ruled by a harsh and suspicious high priest. As they delve deeper, Bentley and Bellamin uncover tensions and hierarchies within the subterranean culture, seeing firsthand the oppression of the enslaved Mole People, who labor tirelessly under their brutal overlords.

The discovery quickly turns dangerous when the archaeologists are captured by the high priest and brought before the king. Amidst the intrigue, they find an unexpected ally in Adad, a sympathetic woman of the underground race who questions the rigid norms of her society. Bentley and Bellamin must navigate treacherous politics and avoid becoming sacrificial victims themselves. As they devise a plan to escape, they rely on their wits and limited resources, even while recognizing their interference may alter the delicate balance of this hidden world forever.