After the horrors of Isstvan V, Horus has declared outright war against the Imperium - but in the shadows of the Emperor's Palace, powerful figures convene. Their plan? To send a specially selected team of clade assassins to execute the Warmaster, end the struggle for the throne of Terra before it has even fully begun. What they cannot know is that Horus and his dark allies have already embarked upon an equally sinister plan of their own, and the clock is ticking...

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The Horus Heresy is a war of Space Marine vs Space Marines, but other combatants lurk in the shadows... Here we see the precursors to Warhammer 40,000's Assassinorum temples in action, even as Horus despatches a monstrous assassin of his own.

The eBook edition includes integrated illustrations of characters and events from the story, and an afterword that places the story in context within the series.