As the Great Rift unfolds in the night sky above Terra and daemons walk upon the birth world of mankind, the Primarch Roboute Guilliman returns, heralding a dark new age.

During the breaking storm, Cypher and his band of Fallen escape from the most secure prison in the Imperium. Now loose in the Imperial Palace, they are hunted by warriors of the Dark Angels, forces of the Adeptus Custodes and Imperial Assassins. But what are Cypher's intentions? Can anything or anyone be trusted?

Told from Cypher's own, unreliable point of view, this tale of truth, lies and secrets sees one of the Imperium's most mysterious figures make war at its very heart. But what are the true motivations of the Lord of the Fallen?