I was watching the coolest documentary one night about the formation of the Earth, and the narrator talked about ancient theories of how our moon was formed. One theory is that a planet called Theia hurled through space, crashed into and skimmed across Earth, shaking loose some of its crust which broke off and flew into space creating two moons which later came together to form our only moon.
Being the space nerd that I am, my imagination immediately went into overdrive and all of a sudden, I had the premise for the plot for Daughter of Gods and Shadows, well, a better premise for a better plot, since my original premise and plot pretty much sucked. In this book, an Ancient race fell from Theia when their world was destroyed. This race came to live among the humans and even blended in until such time as the Demon from their world was resurrected in this one. Then, of course, all hell breaks loose.