My Little Pony: Friendship Is Magic Season 9 Episode 17 - The Summer Sun Setback Episode Title:The Summer Sun Setback.Episode Description:Chrysalis, Cozy Glow, and Tirek take advantage of Grogar's absence to sneak into Canterlot and collect information on the use of the bell they recovered in "Frenemies"; at the same time, Twilight Sparkle begins to plan the Summer Sun Celebration, intending to make it special for Princesses Celestia and Luna since it will be the last one before their retirement. She delegates tasks to Spike, Discord, and her friends, while the three villains sabotage the preparations in order to buy time so they can break into the Canterlot Archives and steal a book on the bell. After Twilight's friends fail to solve the problems on their own, she takes charge and coordinates their efforts to get back on schedule. The Celebration goes off without any trouble, and Twilight renames it "The Festival of the Two Sisters" in the princesses' honor. Chrysalis, Cozy, and Tirek return to Grogar's lair with the stolen book, but realize that they have little time to master the bell for their own ends.