The heavenly realm of Angellus and the demon realm Dibérnia were separated by a barrier erected when the angel Einglenn sacrificed immortality to end their ancient war over human souls on the world of Martel. When the celebrated guardian Cello deliberately alters a human's fate for love — a forbidden act — he is cast out as a fallen angel. His friend Luminus, wanting to understand what Cello chose and why, escapes Angellus to find him. His search for the meaning of love may alter the fate of all three worlds.