Where fallen angels battle Hell's demons, find their lost souls, and discover love while hunting for a prophecy that holds the key to either their redemption or their destruction. At twenty-eight, Cassidy Long is happy with her life. She has a job she loves, a great family, and a future open to possibilities. That all changes after she discovers she is the vessel for the immortal soul of an angel cast out of Heaven, and the only way to break the bond is by her death. Spirited away, Cassidy finds herself in the middle of an eternal war and falling for her angel. Rail is captivated by Cassidy immediately, but fears it's only the connection to his soul fueling his interest. He's vowed to never fall in love, but fate has different plans. The more he fights his growing feelings, the deeper in love he falls. Cassidy not only holds his soul, but his heart. Now, he will fight Heaven and Hell to protect her. Heaven abandoned them, but they did not abandon their calling. Once they were the Watchers, teachers, and mentors to human kind. Now soulless and exiled from Heaven, forced into an endless war, some will fall while others rise to find their destinies. They are the Dark Knights of Heaven.