Long before the coming of the Imperium, the kingdom of Ultramar was ruled by Roboute Guilliman—the last warrior-king of Macragge. Even after learning his true origins as a Primarch, the son of the Emperor of Mankind, he seeks to expand his holdings both by word and by force of the XIII Legion placed under his sole command—the Ultramarines. Now, faced with a hostile Imperium in the world of Toas, Guilliman must carefully choose his weapon—otherwise his dreams of a bright future will never be fulfilled.