In the city of Atro, a vengeance organization recruits from beyond the human world. Their newest agent is a shadow spawn — a being composed entirely of darkness, without a human soul to complicate the work. His capabilities are exceptional. When the organization's immortal leader reawakens after a long dormancy, she assigns the shadow spawn a mission that neither of them fully understands yet. The shadow spawn will travel from urban environments to frozen tundras to arid deserts, experiencing a story that escalates in unexpected directions and builds the kind of dysfunctional family unit that only forms around shared dangerous purpose. Side missions expand the mythology. The main story does not go where it appears to be going.