Many people attempt "alternate histories" and yet few, aside from Turtledove and now Garfinkle, have done enough of their homework to make it plausible. Set in an alternate world at an indeterminate time (I suppose you could work it out if you knew the Athenian dating system better), Greece and the Middle Kingdom have been locked in war for generations, nay centuries -- consider this the ultimate Western Logic versus Eastern Vision division to ever come along. Garfinkle understands Aristotlean physics and takes its implications to their greatest "logical" extreme, such as a gun that fires a bolt capable of halting forward motion, thus causing an airborne craft to seek its natural place amongst the elements (metal falls to earth). Due to friend's input, I learn that his knowledge of Taoist physics, while slighter, is also sound. The flight to and through the celestial spheres is exciting, well concieved, and plausible given the science base of the era. Even more important, however, is the development of the characters. Each is fully rounded, lovingly crafted, and a true joy to journey with. One can only hope that he writes more, not in the same world, but in the same vein. This is one of the best science fiction books I have ever read!