A parallel worlds novel, one of a series of four set in a common setting of the "Imperium". Being an old-fashioned hard science guy, the elements of mysticism woven into this story were for me distracting, but I believe most modern readers would have the opposite complaint - that the magic isn't magic enough. The hero is whisked out of normal life and sent off to travel between parallel universes trying to correct a great imbalance in the entropic forces in order to avert an apocalyptic disaster. Much of this story is very similar to Robert Heinlein's "Glory Road".