Amaranth awakens in a field with an owl griffin protecting her from Chrom and his Shepherds. She discovers her memory is wiped and she has a bump on her head. She joins the Shepherds after exhibiting the qualities of a mage when they defend a nearby town from Plegian bandits. After gaining an alliance with Regna Ferox, the Shepherds move to fight Plegia's forces and revenant monsters called the Risen, and are aided by a masked man calling himself "Marth". Who is this masked stranger? Will Amaranth ever regain her memory?