Two Plegian dark mages find themselves aiding the prince of Ylisse, Chrom, and his Shepherds after they abandoned Plegia. Things get complicated quick, with tensions between the two nations rising. War is inevitable. But what happens when people from one of these black mage's past start showing up? To make matters worse, they bring news of an old enemy chasing after him!

The newly married Corrin and Azura face many harsh challenges ahead... and the war won't be easy either! Warning: spoilers for Invisible Kingdom, readers beware.