Fan Fiction

I've just viewed a movie that I thought had a lovely premise but suffered from weak science, poor film editing, and recovered only about half the costs in the box office. "The Space Between Us".

I do so want to write a Fanfiction story that rounds the story out, but the more I look at doing it the more sinister the penalties seem.

I think I see quite a lot of it here that is Fanfiction based on video games.

I wonder how the authors stay out of trouble?

Gwen