The XIII Legion warship Courage Above All, Guilliman's temporary flagship, broke Warp at the system's edge, at the head of a large void armada consisting of 41 vessels. On Davin, Sanguinius was trapped within a Warp portal and did battle with the daemon Madail while Guilliman and El'Jonson desperately tried to reach him. A vicious battle erupted both on Davin and above it, in which Guilliman's acting flagship Samothrace was destroyed by the Daemonship Veritas Ferrum.

Separate and inviolate in the east, and a great power within their own right, the Legion's very existence made them a threat to the Traitors' conspiracy that could not be ignored, and later on Calth would the Warmaster's plan and the Word Bearers' desire for revenge see that threat destroyed.

During the battle that erupted at Davin's Temple of the Serpent Lodge, the place where Horus had been corrupted by Chaos, Guilliman and El'Jonson finally managed to put aside their lingering emnity and fight together as brothers should, defeating a massive Soul Grinder. The XIII Legion's cruisers and battleships ran abeam of the enemy fleet for repeated exchange of broadsides, offering targets too big and powerful to ignore, while the rest of the Ultramarines fleet used calculated Lance strikes from safer range. The armada then divided its assault potential, doing its utmost to destroy Lorgar's flagship Fidelitas Lex, and attempted to take the World Eaters' flagship Conqueror in a boarding action. In orbit of Terra, Horus' allies delivered the fateful news to the Warmaster while he sat directing the battle for the Imperial Palace. The Ultramarines, Dark Angels and Space Wolves Legions were only solar hours away from reinforcing the Emperor and His Loyalist defenders. Horus knew that his gamble had failed.

In the wake of the Battle of Calth, the Word Bearers Legion, led by Lorgar, linked up with Angron and his World Eaters Legion to launch a Shadow Crusade against the Realm of Ultramar's Five Hundred Worlds in an attempt to spread the massive Warp Storm known as the Ruinstorm that had been conjured by the Word Bearers' First Chaplain Erebus at Calth across the Eastern Fringe. Roboute Guilliman to his gathered Chapter Masters (duty servo-transcription, hours prior to the Battle of Calth Roboute Guilliman (pronounced Ruh-BOOT-ay GIL-li-man), sometimes referred to as the " Avenging Son," " The Victorious," " The Master of Ultramar" and " The Blade of Unity," is the primarch of the Ultramarines Space Marine Legion and its myriad subsequent Successor Chapters. He is the current lord commander of the Imperium and the ruling Imperial Regent. Both were of equal weight and value, one complementing and informing the other, blending together as the metals which made a fine blade. This became the Legion's doctrine and creed.The crusade included the deployment of 100,000 Space Marines, 8,000,000 Imperial Army troops, and thousands of Imperial starships and their support personnel. The Ullanor Crusade marked the high point of the Great Crusade's vast effort to reunite the scattered colony worlds of humanity. Both primarchs fought without heeding their warriors, their godlike movements an inconceivable blur to the Space Marines fighting around them. None had ever imagined the heroes of this new age would take the field against each other, nor could they have predicted the wellsprings of spite between them.

Namorita is a younger clone of Namora. She poses as Namora's daughter, as cloning is illegal in Atlantean culture. She has the gift of flight like her relatives, and teams up with Namor many times, with the two forming a sibling-like bond. Namorita is also best known as a founding member of the New Warriors. As with the society Roboute Guilliman had built on Macragge, the XIII Legion under his mastery would be as ruthlessly even-handed as it was efficient, with the needs of the individual sublimated to the greater whole, but the life of the individual never spent wantonly or without purpose; for the doctrine stated that each Legionary lost weakened those who remained. Thanks to the widely distributed efforts of numerous Imperial Iterators, the story of the Primarch Roboute Guilliman, his early life and his finding is widely known and well accounted for, in stark contrast to certain others of the primarchs. Aquaria Nautica Neptunia, AKA Namora, is the adult cousin of Namor and, in a reversal of Namor's heritage, she is the daughter of a human mother and Atlantean father. She fights alongside Namor until her apparent death at the hands of an evil Lemurian named Llyra Morris, AKA Llyra. Years later, Namora reappears as part of the Agents of Atlas, a group of globe-hopping, old-school heroes.The capsule containing the developing form of one primarch fell upon the world of Macragge in the Eastern Fringe of the galaxy. Macragge was a bleak but not inhospitable world, part of a decayed star empire of ages past that Mankind had inhabited for many centuries since the time of the Dark Age of Technology.

Named Illyrium, it was a barbarous land of outcasts and petty, warring micro-states that had long harboured brigands and mercenaries who raided more civilised lands as often as they hired themselves as foot soldiers to fight their neighbours' wars. Guy: There are so many! We want there to be lots and lots of characters, just like in the Horus Heresy. We want a new generation of heroes like Garviel Loken, Sevatar, Garro and all the rest, those characters that writers can follow through this grand undertaking. I introduce a bunch in Avenging Son , some of whom are already known, such as the Lady VanLeskus, Fleetmaster of Fleet Tertius. There are also many completely fresh ones, like Messinius, a grizzled White Consuls veteran, Ferren Areios, a newly-awoken Primaris Space Marine, and Fabian Guelphrain, one of the Founding Four Historitors.

As the Indomitus Crusade begins, fleets of mighty warships leave Terra on a vital quest to stabilise Imperium Sanctus in the wake of the Great Rift. The returned primarch, Roboute Guilliman, leads a huge force towards the shrine world of Gathalamor, where stable warp routes will allow the flotilla to spread across the beleaguered southern half of the Imperium.