Carrot and Derpy comes across an old book detailing of a door that appears in random locations all around Equestria every hundred years or so. Carrot isn't sure that the legend is real but Derpy's interest is peaked and in dragging her reluctant friend along, both set out to find it in promise of adventure and discovery. But some things are best left alone when they unwillingly awaken a thousand year old grudge that has its eyes set on all those who went against it. When the elements are rendered useless and the princesses are unable to protect their beloved subjects, the fate of Equestria and the rest of the world falls upon the hooves of the unlikeliest of mares.