Twilight is giving a presentation at the Canterlot Magical Conference when a dimensional portal draws her to a parallel dimension full of humans. She decides to seize on the opportunity to write the greatest letter to Celestia ever, by learning all she can about the human dimension while trying to teach them about the magic of friendship. During the information exchange she uncovers the differences between pony and human and how they lost their own elements of harmony. Meanwhile, back in Equestria, Twilight's friends attempt to recover the lost unicorn; but first they need to figure just where she is!