Vigilance. The mission to safeguard Nikki Youngblood depends on the fragile alliance of two half-angel, half-human guardians, both struggling with intense feelings for the girl who has been assigned to their care. Mace, steadfast and deeply in love, wants to protect Nikki at all costs, while Raven's loyalty to Nikki finds him advocating for her independence and battling his own darker inclinations. At the same time, Nikki finds it harder and harder to choose between the two heavenly beings she may never have. Dangers intensify, and tensions between Mace and Raven flare as the purpose of their mission becomes clear. Can their defenses hold up to master manipulator Damon Vessler and the powerful secret he holds regarding Nikki's heritage? Can anyone protect Nikki from her true purpose and destiny?