Struggling with fate, and trying to add to my novel

So, what do you when inspiration strikes like lightning, setting field and forest both aflame at once?

I started editing Part 1 of my novel, Subtraction. I knew Part 2 was missing (did that mean it was subtracted?) and hoped I might soon figure out where it belonged. So Part 1 grew, and grew longer, and I liked it very much. Then I got stuck. Which is what I meant about flaming fields and forest.

Part 1 is my forest with branches interwined - Andrew is teaching math to a special needs...