A mysterious visitor requests a private meeting with Princess Twilight Sparkle to discuss an urgent friendship problem, but when the dust settles, Starlight discovers only an unconscious Twilight left. When she wakes, she can't seem to recall anything. She doesn't remember who she is, what she's done, or even what an alicorn is! Starlight promises to return Twilight's memories to her, enlisting the help of her friends to bring Twilight back.