Born into riches, Probator Symeon Noctis attempts to atone for his past sins by championing the powerless of Nearsteel district. But the sprawling city of Varangantua is uncaring of its masses, and when a bisected corpse is discovered in the neutral zone between Nearsteel and the Adeptus Mechanicus enclave of Steelmound, Noctis finds himself cast into his most dangerous case yet.

Partnering with the tech-priest Rho-1 Lux of the Collegiate Extremis, Noctis is drawn into a murky world of tech-heresy, illegal servitors and exploitation that could end his career, or his life.