I have several pages of notes and questions for myself to ask along the way; I have several as yet unresolved issues that will need to be addressed during the course of this tale.

I have a fair grasp of who my protagonist and antagonist are, as far as their personality types and general demeanor and how these two players are connected.

I know what the final denouement scene MUST look like.

I know I am going to write this in multiple 3rd POV, and how I am going to break up what is very much a time limited plot.

I sit here, pen in hand, and stare at the skinny black lines on the white page and...nothing.

You will, of course, wind up rewriting it, but it will give you something solid on the page, and may even reveal where you need to start, and what needs to happen in between.

For the first draft, I wouldn't worry too much about the opening. Think about how you simply need to get your characters to the denouement. What do they need to do? What do they need to learn to get there to make the choices you want them to make? How do they get to where they need to go?

Another question to ask: what are your characters doing the moment the change happens--the moment they receive their first call to action, if you will. Then start working out that scene.

I'm reminded of Stephen King's It. It begins with Georgie getting obliterated by the clown... which is the beginning of the story for Bill Dunborough.