A Horus Heresy novel

As Calth burns, the Word Bearers and World Eaters begin a bloody crusade across Ultramar. Worlds will burn, legions will clash... and a primarch will fall.

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It's finally revealed why Lorgar didn't lead the assault on Calth... because he's burning his way across Ultramar. But why, and why is Angron with him? Mysteries abound, and primarchs meet on the battlefield...