Far out on the Eastern Fringe, the realm of Ultramar stands alone. Roboute Guilliman has steered the Ultramarines through the horrors of the Shadow Crusade, and is now planning a brighter future. With the arrival of more and more fugitives from the war that has engulfed the rest of the galaxy, all distinction between friend and foe is lost. Isolated from Terra by fearsome warp storms, is Guilliman making a bid for power to rival even the renegade Warmaster Horus?