Lyra is rushing to the cold, far North, where witch clans and armored bears rule. North, where the Gobblers take the children they steal--including her friend Roger. North, where her fearsome uncle Asriel is trying to build a bridge to a parallel world.
Can one small girl make a difference in such great and terrible endeavors? This is Lyra: a savage, a schemer, a liar, and as fierce and true a champion as Roger or Asriel could want--but what Lyra doesn't know is that to help one of them will be to betray the other.
As a passionate believer in the democracy of reading, I don't think it's the task of the author of a book to tell the reader what it means.
The meaning of a story emerges in the meeting between the words on the page and the thoughts in the reader's mind. So when people ask me what I meant by this story, or what was the message I was trying to convey in that one, I have to explain that I'm not going to explain.
Anyway, I'm not in the message business; I'm in the "Once upon a time" business.