In this alternate history, city-sized juggernauts travel the world, over sea and sometimes over land, each representing a country. Britain's juggernaut, the Worldshaker, is commanded by Magnus Porpentine, Col Porpentine's grandfather. When Magnus declares that Col is his successor, it seems that Col's life is truly about to begin. Except there's the matter of the Filthy girl who sneaked into his cabin one night...
See in the world of the juggernauts there are the elites, a couple thousand of the best families and a few skilled craftspeople/technicians and Menials, who reside in the upper decks. Then there are the Filthys, the purportedly barbarous animal-like humans who live in the Bottoms, shoveling coal and occasionally being conscripted to be Menials.
As one might guess, the only difference between the Filthys and the elites is hygiene, the so-called differences a convenient propaganda cooked up by someone (it's not quite clear who) in order to enslave a workforce for the juggernaut.
When Riff, a Filthy girl, hides in his room one night, Col begins to realize that that everything he thought he knew about his life is based on lies.
The underlying premise of Worldshaker is strong. The problem is that the execution is simplistic. In fact, this reads more like a middle reader book than YA. Perhaps that's because my taste in YA slants more towards Holly Black, and because Col, the protagonist, is by definition, naive. But the writing felt more like that in the first two Harry Potter novels. Col is sixteen, but his interest in Riff is too innocent, completely devoid of the hormonal hijinks you'd expect with a teenage boy.
But a bigger issue is that Col's transformation from well-bred, well-behaved boy to revolutionary is flat and lacking emotional depth. Probably because he never really seems that happy with his life in the first place. There's really nothing particularly appealing about life in the Upper Decks; the people are rich and idle, so much so that you wonder why they don't just throw themselves under the rollers of Worldshaker just to end their ennui.
Then there's the fact that there are only a couple thousand Filthys to ten thousand Upper Decks dwellers. In any real society, it's always the reverse, with a large population of underclass supporting a few upperclass.
There are, however, some fast paced and exciting moments in the later half of the book, which is why this wasn't a DNF.