The Raven Guard, under the command of Corax, gathers all remaining loyalists under their banner, intending to repel Horus and his heretics. In the industrial hell of the underhive, the XIXth Legion receives a lesson in tactical mastery from one of their most unlikely enemies - the Night Lords. The sons of Curze are said to be the dark reflection of the Raven Guard, but how far apart are the two Legions really? Or are they closer to each other than the warriors of the Nineteenth are willing to admit?