The Purge: Behind a Loyal Mask (also appears in "The Horus Heresy: Word Bearers eBundle")
The Shadow Crusade spreads across Ultramar, with the Word Bearers 34th Company falling upon the isolated world of Percepton Primus. As the fighting draws out into a programme of extermination, embittered commander Sor Talgron begins to question his part in Lorgar’s grander scheme – for one who stood beside primarchs and high lords in the grand halls of the Imperial Palace, what glory can there now be in punishing Guilliman’s upstart sons? But the price of doubt is known all too well, and if the Word Bearers are ever to return to Terra in triumph then they must purge the last remnants of such unbelief from the face of the galaxy...
Khârn: The Eightfold Path (also appears in "Echoes of Ruin", and "Legacies of Betrayal")
In the fighting pits of the Conqueror, Khârn and his fellow World Eaters compete in ever-bloodier contests of carnage and mayhem. As the Butcher’s Nails dig ever deeper into their brains, the Legion have forsaken the Crimson Path. Now they walk a darker, more dangerous road: the Eightfold Path.
Dark Heart (also available as an Audiobook, as part of the "Calth: Audio Collection", and in "The Horus Heresy: Word Bearers eBundle")
When the Word Bearers launched their surprise assault on Calth, it marked the beginning of their righteous campaign of vengeance against the hated Ultramarines Legion. But for one young acolyte of Kor Phaeron, it is not the sons of Guilliman that he seeks to bring low - through infernal pacts and daemonic power he strives to carve out a destiny for himself in the midst of the greatest war that the galaxy has ever seen. The name of Marduk shall be spoken with awe for millennia still to come...
Scions of the Storm (also appears in "Tales of Heresy")
When Horus the Warmaster rebelled against the Emperor, the ensuing civil war nearly destroyed the Imperium. War raged across galaxy, pitting Astartes against their battle-brothers in a struggle where death was the only victor.