The first of a two-book series, with separate plots, but there is a large plot hook planted for the second book.
It opens with the fall of a tower causing a baby to torn across space and time, and cast up on the shore.
Years later, Meb attempts to warn her village of a raid and falls into the sea, where she meets a merrow. Meanwhile sprites, dragons, and fire-beings conspire to remake the spell that had originally raised that tower (and others) and made the world. And a black dragon Fionn is wandering about, mostly in human form, making trouble, telling dragons he's out to destroy the world (they're kinda used it by now).
It involves Meb's first attempt at theft getting her very wet, a lot of rubies, the weaknesses of races to other races, why merrow catch the souls of drowned fishermen, why the dvergar regard an alvar prince as a tax-collector, two alvar seamstresses, making a troll laugh, and more.