In the remote mountains of Croatia, an archaeologist makes a strange discovery: a subterranean Catholic chapel, hidden for centuries, holds the bones of a Neanderthal woman. In the same cavern system, elaborate primitive paintings tell the story of an immense battle between tribes of Neanderthals and monstrous shadowy figures. Who is this mysterious enemy depicted in these ancient drawings and what do the paintings mean? Before any answers could be made, the investigative team is attacked, while at the same time, a bloody assault is made upon a primate research center outside of Atlanta. How are these events connected? Who is behind these attacks? The search for the truth will take Commander Gray Pierce of Sigma Force 50,000 years into the past. As he and Sigma trace the evolution of human intelligence to its true source, they will be plunged into a cataclysmic battle for the future of humanity that stretches across the globe and beyond.