When the sacred gemstone of a Daynovan shrine is stolen during a precision strike by the Umbral Cult, young Daynist acolyte Jesine’s peaceful life is destroyed. Armed with only her healing gift and the blessing of her mentor, she strikes a desperate bargain with Kae, a cynical aeroship captain with a past steeped in war, to hunt the thieves across Una.

Their pursuit leads them into lawless ports, ancient ruins, difficult conditions, and to the one of the cult's many leaders, Boro. This man seeks to corrupt the Beacon and seize the origins of the Heart of Dayna, believed to be the origin of a power that grants eternal life. As the chase drives them toward the world's center, Jesine is forced to confront cracks in her faith and face the truth behind the balance of light and darkness.

To save the gemstone from destruction, Jesine must decide whether light’s greatest power lies in vanquishing darkness... or in healing it.