World War I is now sweeping through the entire world, and the Leviathan is in more danger than ever. 
 And Scott Westerfeld ends his alt-history/steampunk trilogy with a bang (and a blast) in "Goliath," which intertwines steampunk warfare with a very odd love story and a mad scientist plot. Not only does he drag the exiled Austrian prince and transvestite airgirl across Asia, the Pacific, Mexico and right into New York City, but he wraps up their story -- especially the budding romance -- in a thoroughly satisfactory way. 
 While passing over Russia, the Leviathan is sent to pick up a very important person: Nicola Tesla, a Clanker scientist who claims to have invented a death ray called Goliath, which can obliterate an entire city. The evidence: a devastating blast in Siberia. Alek wants to believe that Goliath can be used to intimidate the Clanker powers into ending the war, but Deryn isn't too sure. 
 As the Leviathan travels across Russia, Japan, the Pacific, Mexico and finally the United States, Alek finally discovers Deryn's secret -- and so do a bunch of other people, including a nosy reporter who threatens to undermine the war effort. And as Goliath's grand unveiling approaches, Deryn learns of a plot to destroy the massive weapon -- and possibly Alek as well. 
 The first two books of Westerfeld's trilogy had a lot of historical places and content, but not a lot of actual historical personages. But this one introduces a bunch of them -- Nicola Tesla, Pancho Villa and William Randolph Hearst -- and the major flaw in the story is that some of these feel like distractions from the main plot of the story. 
 The rest of the time, Westerfeld slowly intertwines the various subplots, and slaps a big dramatic climax involving a German Wasserwanderer, Goliath, and a British plot to pull the US into the war. His strong, streamlined prose continues to reveal new aspects of both Clanker (the water-walker) and Darwinist technology (kappas), and he introduces a lot of real tension as poor Alek discovers that he may not even be able to trust his own men. 
 And both Alek and Deryn face turning points -- Deryn realizes that she can seriously damage the war effort if her gender is revealed, and Alek struggles with the question of what his future holds, as well as whom he wants to ally himself with. Westerfeld weaves in their budding romance with a subtle touch, focusing more on passionate protectiveness than on anything too... goopy. 
 "Goliath" gets a bit distracted by the historical cameos, but is otherwise a solid, slow-building finale for this brilliant steampunk trilogy. Smooth, sleek and just a little romantic.