Whew! It took me forever to figure out "whodunit" in my third Marge Christensen Mystery (Who more than Wished You Were Dead?) -- I was three quarters of the way through before Marge discovered who the culprit was, and then I couldn't figure out how she was going to prove it. Every time Marge hit me over the head with an answer, I had to go back to the beginning again to make sure everything hung together.
I keep thinking I'll be smarter on my next book. I'll plan my characters, outline my plot, and know how Marge is getting from here to there. That way I can write straight through one draft before going back and revising. That's the way you're supposed to do it, isn't it?
But then again maybe not. Who's to say that if I plan it all out and know where I want to end up, Marge won't disagree and, in addition to reworking what is already written, I also have to revamp all my carefully laid plans to get where she decides I should go.