"Empire of Unreason" is the third book in the four book "Age of Unreason" series by Greg Keyes. It takes place approximately 10 years after the events of "A Calculus of Angels". Ben Franklin is living back in the American Colonies, in Charleston. He is a founding member of some sort of secret scientific organization called the Junto. The Junto are leaders in the community and they are working to continue to advance science as well as figure out exactly how to stop and kill the malakim, the "demons" that were discovered through Isaac Newton's alchemy and are the ultimate cause of all of the destruction of the past twelve years. The exiled pretender King James has come to the colonies (since London was utterly destroyed twelve years prior) to claim his throne, but Franklin sees the hand of the malakim behind King James.
Adrienne, the woman scientist who has been the driving force behind much of the innovation and destruction of the past decade, is in the court of the Tsar of Russia. She knows there are forces of the malakim aligned against humanity, but she owes so much to others of the malakim who claim obedience to her. She continues to search for her lost son, who would be twelve years old by the events of "Empire of Unreason". While she continues to search for her son, and evade her own enemies in Russia, there is a new force in America. A boy called the Sun King, who has come out of the West. He seems to be a prophet, and leads forces from China. But, he may also be Adrienne's son.
There is so much going on in "Empire of Unreason" that if one hasn't read the first two volumes of this series ("Newton's Cannon", and "A Calculus of Angels") the reader will be completely lost. This book suffers from the middle book syndrome in that it works to continue a story and set up a conclusion, but it cannot stand alone. The reader is thrust right into the story and has to play catch-up figuring out exactly how much time has passed since the second book in the series. While this is a "middle book", it is also a fast paced, exciting story. Greg Keyes no longer has to engage in world building, but can now give us an adventure story that drives to an ending. "Empire of Unreason" seemed to end in a hurry, and was a little confusing, but the "Age of Unreason" series is proving to be an excellent one in the fantasy genre, as well as being an alternate history. Keyes is a very good writer, and he is working with a very broad canvas here. Read the first two books, and then continue on with the series. It is worthwhile reading for the fantasy reader.