Leapin' Leviathan!

Steampunk is a genre of science fiction that puts its speculative technologies, gadgets, mad scientists and adventures smack in the middle of the Victorian era or a little later, fueling them by steam power and adding a healthy dose of Jules Verne design into the mix. The protagonists may be operating in secret from the rest of the world, which explains why their magnificent scientific advances remain unknown today. Or they may be in a parallel universe where things proceeded differently than they did in the real world. Even though it's speculative, it's commonly tech-heavy because important features of the plot often depend on the fantastic devices used by would-be dictators to conquer the world or by brave heroes determined to stop them.

Scott Westerfeld, best-selling author of the young-adult series "The Uglies," takes up residence near steampunk territory with his Leviathan trilogy, of which 2009's Leviathan is the first. In 1914, young Austrian Prince Alek must flee his home when his parents, the Archduke Franz Ferdinand and Princess Sophie, are poisoned. He and a handful of loyal retainers sneak out towards Switzerland in a mechanical walker. It's a small tank something like the machines which helped Imperial Stormtroopers get beaten by sentient teddy bears in Return of the Jedi, only Alek and his crew are not idiots. War between Germany and England breaks out while they are on the run, adding some new political wrinkles to their situation.

At about the same time, young Dylan Sharp takes flight on the genetically engineered, hydrogen-filled whale Leviathan, one of the Royal Navy's finest airships. But all is not as it seems, because Dylan is actually Deryn, a young woman who disguises herself as a boy in order to serve in a Navy that doesn't admit women.

Westerfeld sets his story in the middle of some real-world political events -- the assassination of the Archduke led to World War I in 1914, although none of their children were named Alek. He has just tweaked things a little. He puts mechanized units into combat a couple of years before the first tanks existed, and of course gives them legs instead of revolving treads. And he has Charles Darwin discover DNA ("life threads" in the Leviathan world) in addition to formulating evolutionary theory. Some nations adopt Darwinian practices, breeding specialized creatures to do jobs that might be done by machine. The airship Leviathan, for example, is a genetically engineered whale that carries a gondola and is open enough inside its body to house a crew. These are the Darwinist nations. Others stick to mechanical methods, building the diesel and steam engines we see in our own past, although with some slight differences. They are the Clanker nations and they view Darwinists with some suspicion for their manipulation of lifeforms.

The Leviathan world relies on a couple of implausibilities -- that people would think of engine-driven walking transportation before wheeled transportation, and that a 19th century naturalist using optical microscopes would not only discover DNA but also how to manipulate it in ways modern supercomputers can't match. But throw those out, and Westerfeld builds a logical world whose flavor is subtly different from our own but still pleasing. He also does something some more plausible steampunk world-builders fail to do: Tell a great adventure story. Deryn and Alek are engaging and brave young people, saddled with adult responsibilities while yet teenagers and trying to cope with the challenges their situations present. We can guess their friendship will become complicated once the world learns "Dylan" is Deryn, but that has yet to happen in this first book and so Westerfeld can concentrate on developing their bond.

He also trims away just about anything that would slow his story down; exposition comes in short bursts when it helps move the action along and he almost never commits the Original Storytelling Sin of telling instead of showing. Leviathan is another excellent and thoughtful entry from a top-level young-adult author and a great start for a fun ride.