After the Canterlot Wedding disaster, the rebellious Thorax defected from the changeling kingdom to come to the land of Equestria, and with him came many changelings who agreed with his message of peace. However, Queen Chrysalis, angry at his insubordination, launched an invasion against Equestria.

With their forces spread thin across the land, Equestria has no choice but to rely on one thousand reformed changeling volunteers as an assault against Chrysalis's main army. But will the plan to end the invasion force succeed? Or is hope doomed for all?