Any Clues for The Call.......IMPORTANT......??? written by Robert Westall

heey everyone,

I had to read a small part of a book called the Call
Well, I didn't really get the story, becuase of its undefinable
words and weird story, still it was cool to read, but I didn't
get the clues, so if someone has ever read the book and know
What they really mean with the book and what the clues are
please let me know very SOON.............!!!
thanks in advance