The Empire of Harmony is a unified coalition of various races who joined under the banner of Princess Spike, who lead the combined forces in a battle to defeat a powerful tyrant, and has since been the world's biggest and longest running society.

Big Macintosh is an Earth Pony visiting the city of Canterlot, the capital city of the Empire, on urgent business (and a little sightseeing), however little does she realise she's going to end up at the centre of a race to save the world as an ancient and powerful enemy returns from the past, filled with anger and hate....and power.