In some far distant future year, the human race has spread out among the stars, encountering other species and an Empire that spans at least this corner of the galaxy. The Empire is ruled from the Imperial City of Tenochtitlan (which he know as Mexico City), the capital of the planet Anahuac. But the advance of Imperial Mexica has revealed that there were earlier powerful interstellar empires, which are long gone now, leaving behind their mysterious artifacts.When a survey team goes missing, it's up to Dr. Gretchen Andersen to unravel the mystery, a mystery centered on these ancient artifacts, one that could shake the very foundations of the Empire.