First of all I'd like to mention that the author has mixed physics with magic. "Stealheart's steel didn't rust", what kind of metal it was? Nickel? Gold?
But, avoiding these, the story is pretty interesting. It intrigues the reader from the beginning, the middle part a little boring, and he end is fine.
I'd realized the truth about Prof and Megan somewhere in the middle of the reading. Yes, and another misleading fact-where did they get their maps in their cells? Humanity was left without technology and satellites.