I have an idea for a book/short story , based partially on personal experience.

I first had the idea when I saw a couple arguing in a car parked downtown one winter and thought it would be a great symbol/metaphor to get the book started.

I know what I want to say, but the story I have in my head is extremely controversial. I have no delusions of actually getting published, but for peer review and advice I'm afraid I'd catch some severe criticism for the subject as a whole. Ultimately, I suppose it would wind up as a thinly veiled social commentary.

I guess my problem is I have a beginning and i have a vague idea for an end, but I have no clue how to fill in the middle.

This will only be a part time endeavor, and I'm not taking it super seriously since i don't see this becoming any more than another word document on my laptop, but I'd like to make something I'm proud of. Any advice is welcome.