With news of Horus’s treachery spreading across the galaxy, the Great Crusade grinds to a halt as the primarchs and their Legions decide where their loyalty lies with the Emperor, or with the rebel Warmaster. The Dark Angels, too, face a time of testing, both among the stars and on their home world Caliban. Luther, once Lion El’Jonson’s trusted second-in-command, now languishes as an exile in all but name while his master struggles to thwart the traitors’ advance upon the forge world Diamat. But an ancient evil gathers its strength beneath the surface of Caliban, and the First Legion will soon be thrust into a deadly conflict where all that they know will be cast into doubt.

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The divide in the Dark Angels Legion, between those loyal to the Lion and those who declare for Luther, becomes clear... but even more important might be what happens off Caliban, as Lion El'Jonson battles the traitors for control of dangerous weapons, and then delivers them to the last person you'll expect...

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.