A mystery wrapped in a myth about the origins of humanity. A race to find an ancient pyramid hidden in plain sight. A secret so dangerous its guardians will kill to protect it. And an ancient covenant that might save the world, or destroy it completely. In 1655 a group of explorers from the Emerald Star entered the Namibian Desert in search of an ancient relic rumored to be hidden in a secret temple. None of the crew ever returned - but stories of their mysterious demise continued to be told. In the present-day Turkish subterranean city of Derinkuyu, a strange wooden placard is discovered floating in an old well. It's covered in the script of a language long forgotten, but Sam Reilly has seen the text before. The words suggest an ancient race might still exist, and are in the process of building a new temple. The question is - is it the same temple where Dr. Billie Swan is being held prisoner?