Twilight's been living a charmed life on Butterfly Island. All her friends have reassured her that there's no need to leave the island because everything a pony could want is right here. They're doing it because they want what's best for her, right...?
Then a mysterious, secretive unicorn named Starlight Glimmer arrives to the island, with wild claims that Twilight has been lied to all her life, and the only way to escape her gilded cage is to do exactly as Starlight says. Starlight's a complete stranger to Twilight, but her story is too outlandish to make up. Which means it must be true. Which means obeying her is the right thing to do. Right...?
After all, you can't betray ponies who were never your friends in the first place....