Trixie returns with the alicorn amulet, an object that gives her untold power, and she uses it to get revenge on Twilight. After Trixie drives Twilight from Ponyville it's up to the purple unicorn and her friends to figure out a way to defeat Trixie.
Thanks to some sleight of hand Twilight manages to trick Trixie into taking off the alicorn amulet, restoring her back to her proper mind. The episode ends with Twilight forgiving Trixie for her behavior, during a performance for Princess Celestia and two delegates from Saddle Arabia.
Season three has gotten something of an unfair reputation for being the fan pandering season. The biggest concern being that the writers will get lazy if they have an easy way to appeal to fans. After all, why bother writing a good episode when all it takes is including fan favorite characters.
Fortunately, while there may be a bit of pandering happening with the reintroduction of characters like Trixie, the writers haven't used this as an excuse to get lazy with their writing. The basic story is solid, and the twist behind Twilight's victory is actually surprising and satisfying at the same time. While I don't normally worry about spoilers in my reviews, I'l leave this part unspoiled for anyone that hasn't yet seen the episode.
What really makes this episode stand out is how much of a more effective villain than Sombra Trixie was. I know, I know, making fun of Sombra is old hat at this point. But it's true, Trixie actually succeeded in her goal, for a short time, and was defeated in a much more interesting manner than Sombra. It also helps that she has a lot more personality than Sombra.
The other stand out in this episode is Fluttershy. She has some of the best moments of the episode, from the opening scene to her one pony mission to contact Twilight. I may be biased, but with the exception of the finale, Fluttershy's scenes were easily the most entertaining in this episode. And while the episode is best enjoyed by fans that were waiting for Trixie's return, it's easily enjoyed by most anyone.