They say there are three universes. A trinity. Three paths originating from the same point, but diverging heavily along the lines. One contains Equestria, homeland of ponies and their magic ways. The other, humanity, where technological progress rules the day and night. But what of the middle-child, you could say? What of the universe that lies in between?

One where ponies and humans have always lived together.

Twilight Sparkle and five companions are about to be granted a rare view of this world, in particular the United Equestrian States of America, circa the 1940s. For this universe contains more than just humans and ponies; it also, because of some strange twist of fate, contains counterparts to many ponies in Equestria. Including one: Twilight Spiritsong, voodoo priestess of New Orleans.

And she wants something from the Twilight next door.