The second book in The Horus Heresy Primarchs series, Chris Wraight’s Leman Russ: The Great Wolf is, like David Annandale’s Guilliman novel, not an origin story. It does however deal with the origin of a key part of the Wolves’ background – their rivalry with the Dark Angels. During the Great Crusade, the VI Legion were tasked with the pacification of the Dulan empire, who refused compliance with the Imperium. In the final stages of the campaign Russ and his brother Lion El’Jonson famously came to blows, and now we get the story of why that happened…at least from Russ’ perspective.
