I left it alone for while, because the third act wasn't coming together properly. When I went back and reread what I have of an outline, I discovered that I had unwittingly set up one of the background characters to be the "unexpected-but-actual" villain.
Now I have to decide if that will work (part of my brain says, go on, use it!), or whether I need to rework a bunch of the first two acts as well.
Writing's fun. :-)