With their crusade against the Night Lords reaching its height, the Dark Angels find themselves thrust into a new battle. Beset by daemons and forced to choose between two brother Legions, the Lion's loyalties will be tested and a secret will be discovered that could change the face of the war, and the destiny of the Dark Angels Legion.

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The Lion is finally forced to choose as a side as the Iron Hands and Death Guard come to blows over a mysterious artefact. And when he claims it for his own, the Dark Angels primarch sets his Legion on a course that will haunt them for ten thousand years.