Realizing that the Everfree's creatures are migrating for the first time in centuries, Twilight Sparkle gathers a team together to follow the vicious monsters to their new abode. Unfortunately, it leads right to a place of strange origins, what the ponies have dubbed as the "Mysterious City". Nopony who goes there ever comes back, nor do any ponies originate there. Why are the monstrous, vile, woodland critters packing up shop, and exactly who is running the show at the "Mysterious City"? Griffins claim innocence from its creation, Diamond Dogs don't know any better, and the other pony countries are just as confused. Twilight's job is to make contact with the "Mysterious City" and report her findings to Princess Celestia. Just what will she find?