I just realized that I don’t have to start my synopsis from scratch. I already have a place to start.
My query letter includes both the “back of the book” description and a slightly longer description that has a bit more depth. That description is where I’m going to start. It doesn’t have the end of the story, which I need to include in the synopsis, and several major plot points are vague out of necessity. I think that taking those places and adding details will be exactly what I need to do to get a draft of the synopsis done.
As always, I’ll keep you updated.