Sunset Shimmer had used her magical powers to save the human world from many villains and was given a lot of hope when she no longer treated like a villain but as a friend.
One night, while Sunset and Twilight were fast asleep after spending the night at Pinkie's house after a difficult exam, three orbs of blue light enter through the window in their room and after landing on the desk next to Sunset's side of the bed, they dissipate.
The next morning, As Twilight is getting ready for breakfast, she noticed a blue ring on her bed-side desk, Sunset and Pinkie noticed one on their's to.
They both soon learn not only that the rest of the girls have similar rings too, but that these belonged to groups known as lantern corps. And they are transported to their respective corps.
What will happen next only time will tell.