What is the theme in Hush, Hush by Becca Fitzpatrick?

Another theme in the book is Nephilim. Nephilim are a race of half-angels, half-mortals. The origin is Biblical in nature. The story of the angels falling from heaven is legendary. Supposedly the angels sent to watch over the Garden of Eden became lustful and hungry for power; seeking to rule what lay beyond the boundaries of Eden. Because they defied their earthly purpose, the angels were stripped of their wings.