Every once in a while I'll be in the shower or eating or driving and an idea for a story will pop into my head. Oh man, it's so fun when that happens. What often ends up happening is that two or three of my story ideas will merge into one story with several facets. Let's say that I come up with an idea for an interesting character. Later on I may come up with an interesting scenario. Maybe it would be really cool to put that character in that scenario and see where the story goes from there.
That is what happened with my idea for the Nocent. Several ideas dating back all the way to stories, songs and poems I wrote in high school to dreams I've had over the years, culminated into one huge story. Many of the short stories and poems served as background for some of the characters. Many nightmares I've had became actual scenes in the book. I already knew it was scary because of how it affected me while I slept.