Rainbow Dash has everything a pony could want: great friends, a decent job, and a promising future with the Wonderbolts, but something's missing. Something keeps nagging at the back of her mind, something she's forgotten.

When an ancient prophecy comes true, and a mysterious unicorn appears in Ponyville, it seems like an easy job for the Elements of Harmony. But how does this unicorn know so much about Rainbow and her friends? How is she always around when something important happens? Why won't the elements work anymore, and most importantly, what is it that Rainbow Dash can't remember?

Can the five Elements of Harmony defeat Twilight Sparkle before she fulfills the prophecy and destroys harmony in Equestria forever?