Aleksander, son of Archduke Franz Ferdinand and his wife Sophie Chotek, is pulled from his bed in the middle of the night to practice night maneuvers with the walker. It's not long before he learns the truth from his teachers: his parents have been assassinated, and they need to get out of Austria quickly. Alek has very little time to learn how to pilot the giant machine in the dark. He also has to avoid detection, and when that fails, escape any and all attacks without getting himself or any of his men captured. He may be the rightful heir, but nobody can know--at least right now, on the brink of war--that he still survives. 
 Meanwhile, Deryn is desperate to pass the tests to become a midshipman in the Air Service. The only problem she might have is that they don't allow girls, so she enrolls in the testing as Dylan--and when a runaway hydrogen-breather takes her on an impromptu tour over London, she proves her mettle enough to be admitted. As long as her superiors don't find out she's a she. 
 Eventually these two meet up, both in rather dire straights. Deryn's British, Darwinist officers are all for keeping the strange Austrian Clanker under lock and key, but he may hold the keys to their salvation--just as they can help his escape. Deryn, Alek, and their respective crews have choices to make: do what's best for their countries in this new war, or what's best for their new, though unlikely, allies. 
 Westerfeld's latest series treds new ground for him, breaking into the Steampunk genre with this alternate history of the World War I. Unfortunately, Westerfeld is less confident here than in his other settings; the world setting fails to come alive the same way as his other books. Deryn and Alex and just about the only characters (there are others, but even the most major of these are background) and even their development is a little thin at times. 
 I've no doubts that this book will circulate, particularly among middle-school boys, but this Westerfeld fan was disappointed. It reads younger than his other books (maybe 5th-8th grade?), and the pictures throughout don't help. On the bright side, if I could get posters of the endpapers, I'd frame them and hang them everywhere. Too bad the interior illustration doesn't hold up to the promise made by the jacket art and endpapers.