So, I'm cranking along on the current book-in-progress, Bristlecone, about a couple of retired secret agents. That was the genesis of this one, the characters, and after noodling around a bit -- I usually do a brainstorm page where I just toss out everything that floats up from the murky swamp in my head -- I got the title, and the name of the villain, and a kinda-sorta notion of a MacGuffin.
(For those of you interested in what that is, go here. If you don't want details, the MacGuffin -- sometimes "McGuffin" -- is a device of some kind that gets the plot rolling in a story. It may or may not have another function than that. Consider The Maltese Falcon. Or the Letters of Transit in Casablanca. They aren't really what the movies are about, but you need them.
Alfred Hitchcock either came up with the notion or was the first to make it generally known.)
I went for the classic mystery-man-with-a-gun, which while not technically a MacGuffin, is close enough.
There's a bit of advice pulp writers used to offer to newbs: If you are stuck in a scene and you don't know how to get out of it, have somebody kick open the door and come in shooting.
So I just kicked open the door, and started shooting, doing scenes I knew I wanted to have, without any real idea of what the villain was up to. He was around, doing something villainous, and what the caper was? It wasn't required at this point -- I didn't really need to know in order to get the set-up going. And in an odd way, that's good, because if I didn't know, the audience wasn't likely to know either, so if I don't rewrite the early stuff to offer clues, no way they can figure it out until later.
I knew that my old retired couple, Hull and Khadra, were going to be dragged out of a comfortable retirement against their wishes. I knew bodies would start to pile up, and I was consciously reconsidering the first novel I sold, The Tularemia Gambit, as a template for this one. Because when I wrote that novel, I was a newb, but I'm better now, and I expect I could put some nice spin on the story.
It's not as if that's going to cause problems, using anything from Tularemia. The six people who read that book -- judging by the sales -- aren't going to cut into my potential audience a whole lot. Plus it's not a mystery. The bad guy is going to reveal what the caper is early in the book, and then it's a race to see if he can pull it off or they can stop him.
Got almost five chapters in before I realized what the bad guy was up to.
Fascinating how warped a writer's mind is, and how many ways there are to run at a story.
P.S. Don't ask, don't tell, viz. what the bad guy is up to. Suffice it to say is is wicked-evil-bad.