twilight acidently stubles upon a portal leading to dark cave revealing four new portals. her and rainbow dash dicover these new worlds not only hold different species, but also dark and dangerous anti-harmony spirits that riegn over two of the worlds. as the spirits discover the two ponies, they also discover the other two worlds. when twilight and princess celestia realize the elements of harmony wont be enough to stop them, they realize there more to magic then they realize.