Far away on the Eastern Fringe, the realm of Ultramar is unparalleled. Having withstood the Word Bearers' attack on Calth and the subsequent Shadow Crusade on the Five Hundred Worlds, Ultramarines Primarch Roboute Guilliman gathered all his loyal troops to Macragge, where he decided to consider the future of humanity. With the arrival of more and more people fleeing the war engulfing the rest of the galaxy, the line between friend and foe becomes blurred. And now, with Terra separated from Ultramar by raging Warp storms, will Guilliman be able to muster enough forces to confront the traitor Warmaster Horus?