I'm Stuck

I've been stuck for a few weeks trying to solve an issue with my latest book. I know there's something wrong, my first reader confirms that there's something wrong, but I'm not sure how to fix it. When I run into this problem I usually ask myself what the protagonist wants, and if I don't have a good answer for that question then that's probably the issue. In this case, I did have a good answer. So, I had to start considering other issues. In the end, I think the big problem was with the details of the mystery. There just wasn't that much tension. I've spent today rejigging a few things and now I think (I hope) I've got it sussed out.