Welcome to the United States of America in the 1880s: Settlers are moving west, as do the iron horses that bring them by rail ... and somewhere in those vast regions of deserts and native tribes, a darkness is gathering. Calls Thunder Song, a powerful Shoshone shaman, senses it first, and reaches out to the Western Council, an association of magi and other magical folk, for possible insight and assistance. In response, the Council sends a single magus, Aquinas Moore, as a token gesture, but what starts as a simple diplomatic mission for Aquinas turns into a struggle for existence against a foe more terrible than any of them has ever encountered, which has already infiltrated the halls of power. Now, these unlikely allies must band together with a pair of Native American deities and a dead man to fight off a threat from outside the universe, a threat that intends to not only conquer, but change the very nature of existence.