A good, dramatic entry in your story series... :)

I know at this point you're still looking for "overall structure," but I'll just try to encourage you to prime your thinking about one thing as you move forward with your book project:

Before you "pull the chain" and actually publish your book, please have more than one set of eyes read it for typos and for details of grammar, sentence structure, and so forth. Why?

We live in a brave new world where almost anyone can self-publish a book. The Amazon Kindle is an amazing device, and there are writing structuring tools such as Scrivener that take a lot of the pain out of self-publishing. However, one of the unfortunate consequences of this has been an explosion of poor quality reading material on the market.

I personally believe it is hard to overcome the bad first impression made when a book contains rank amateur errors in spelling, word usage, or grammar that could have, should have, and would have been caught by the right collection of proof-readers.

In other words, measure twice; cut once. ;) Just my two cents along with my best wishes. :)