After the collapse of civilization, gen-modded humans live in villages watched over by benevolent artificial intelligences and harshly judged by human-AI hybrids called plague birds. The plague birds' judgement is swift and deadly, as Crista discovered as a child when she watched one kill her mother.Years later, to save her father and their village, Crista must become what she-and all humans-fear, a plague bird hosting a killer blood AI. Red Day, Crista's new AI symbiont, tasks them with avenging the death of its former host. They leave the only home Crista has ever known to hunt down the Veil, an ancient group of magic-wielding murderers. As they travel farther from home than Crista ever imagined, she's plunged into a world where she is judging and executing wrongdoers, befriending other outcasts, and discovering truths that make their mission much more personal.