I used to think it was somewhat cliché for a writer to claim that characters 'arrived' in her head and needed to be written 'their way'. I know better now and would add that one of the great joys of writing is discovering where the story is going before anyone else does, as it unfolds on the page.
I have some interesting places to go in Book II.
Very close to the end of Book I. Writing the last 1000ish words today and tomorrow.