A pair of monastic siblings struggle to help a sentient spaceship suffering through an existential crisis in this philosophical novel about what constitutes life, love, humanity, and death for fans of Martha Wells's The Murderbot Diaries and The Deep Sky by Yume Kitasei.

Unable to forgive himself for his actions aboard the Counsel of Nicaea, Iris left the religious Starlit Order. People died, he lost his heart to a man of science, and he sacrificed his best friend-an implanted AI companion-to shut down the murdering consciousness birthed within the spaceship. Still devoted to serving others, Iris labors aboard a space station near Nicaea's husk, a reminder of his frailties and his failures.

Vessel Bacai believes that leadership of the Northern Temple of the Starlit Order is hers by right of inheritance. But her adopted brother Iris was always their late mother's choice, despite having no ambition to assume the role. Bacai needs Iris to officially step aside so she can continue the holy work he selfishly abandoned.

Iris also left his work on the Nicaea unfinished. The ship has awakened, attacking the space station without warning, harming its inhabitants. And the ship sends Iris a message, begging the former Vessel to end its suffering-by helping it to die.

Now, Iris is returning to Nicaea, accompanied by Bacai and a science team-including the beloved engineer he left behind, Yan Fukui-to confront a sentient AI that understands the behaviors and emotions that drive human nature . . .