It turns out that Sunset Shimmer's final letters to Princess Celestia before her exile were not filled with resentment or remorse. There might have been a lot more frantic running away involved. But it was definitely not Sunset's fault. At all.
Sunset manages to prevent Twilight from going completely crazy after she opened her magic stealing device and because of that Twilight manages to keep the pony power.
2 weeks after Camp Everfree ended, Sunset and her friends are excited to start the Fall semester with their newfound powers. However, Sunset soon realizes that the abilities they've been given could send their friendships, and their lives, into ruin.
Halfway through the Friendship Games, Twilight realizes exactly how powerful her pendant is and enlists a more magic-experienced person to be her co-scientist.
After developing a new portal that can explore other dimensions, Twilight and Sunset are pulled into an adventure, where they meet even more doppelgängers of themselves. Together they have to save the day, and learn about each other in the process.