A Calculus of Angels (The Age of Unreason, Book 2)

1722: A second Dark Age looms. An asteroid has devastated the Earth, called down by dire creatures who plot against the world of men. The brilliant-- some say mad--Isaac Newton has taken refuge in ancient Prague. There, with his young apprentice Ben Franklin, he plumbs the secrets of the aetheric beings who have so nearly destroyed humanity.
But their safety is tenuous. Peter the Great marches his unstoppable forces across Europe. And half a world away, Cotton Mather and Blackbeard the pirate assemble a party of colonial luminaries to cross the Atlantic and discover what has befallen the Old World. With them sails Red Shoes, a Choctaw shaman whose mysterious connections to the invisible world warn him that they are all moving toward a confrontation as violent as it is decisive . . .