The book is set in an steam-punky alternate-history World War I. The Germans and their allies are the "Clankers"—relying on giant walking mechanical war machines. The British are "Darwinists"—using genetic engineering to create all sorts of creatures, including the titular whale-based airship.
We get to see these different realms through two very different protagonists. Alek is the son of Archduke Franz Ferdinand, and as you might expect in a book about World War I, he's an orphan by the end of the first chapter and is soon on the run from his father's political enemies. Deryn is a young British woman who has disguised herself as a boy in order to join the British Air Service.
It's a rip-roaring adventure. Westerfeld does action scenes like nobody's business, and there's plenty of that, but there's also all your great bildungsroman elements as Alek, especially, begins to grow from a child to privilege to a young man with a weighty responsibility on his shoulders.
The only thing wrong, at all, with the book is that it's the first of a trilogy and so I'm going to have to wait years, likely, to read the whole story. And this book definitely ends on a cliff-hanger. Can they evade the (spoilers)? What's going to happen to the (spoilers)? And what are the (spoilers)?
FuzzyCo grade: A+