Sixteen-year-old Col Porpentine is the grandson of the supreme commander of the city-sized ship Worldshaker and has just been named his successor. But Col's rarified world is turned upside down by a girl named Riff, who is a Filthy--Worldshaker's lowest class, confined to the bottom deck as laborers. Col has always been told that Filthies are practically beasts, but Riff is smart, confident, and beautiful.  As Col begins to secretly spend more time with Riff, he begins to question everything he was raised to believe was true, and realizes that if Riff is right, then everything he was raised to believe is a lie. Ages twelve and up.