You're right at least about the mystery part. If I can get myself to stop thinking about it and put it aside, the rest can easily be worked on without being affected by whether or not there's a mystery being solved in the other part.

But the other problem, about changing the location and action of the story, has to be dealt with now, or very soon. And it's making me nuts! I could just skip the entire 2nd half of the story and write the rest, I suppose....