A Canterlot Wedding - Part 1 / A Canterlot Wedding - Part 2.The Mane 6 are summoned to plan a wedding for Shining Armor, Twilight's older brother and captain of the royal guard at Canterlot, and Princess Cadance, her childhood foalsitter. Twilight becomes suspicious of Cadance when the princess fails to remember her, and even more so when Cadance continually puts down all of her friends. When her friends refuse to listen to Twilight's accusations, Twilight attempts to warn Shining Armor, only to witness Cadance place a seemingly evil spell on him. Twilight accosts Cadance at the wedding rehearsal, causing her to break down in tears. Furious at Twilight, Shining Armor bans her from the wedding, while her friends and Princess Celestia leave her to reflect on her actions. When Twilight tries to apologize to Cadance, the princess uses a magic spell that teleports her underground.
A Canterlot Wedding - Part 2: After being trapped in a cavern by Cadance, Twilight encounters another Cadance and learns that the princess who Shining Armor is about to marry is actually an impostor. Twilight and the real Cadance escape in time to stop the wedding, where Cadance exposes the impostor as Queen Chrysalis, the leader of the shapeshifting changelings. Chrysalis reveals her plan to invade Canterlot, having taken over Shining Armor's mind and weakened his magic shield that protects the city. She is able to defeat Princess Celestia, and her army prevents Twilight and her friends from retrieving the Elements of Harmony to stop her. As Chrysalis celebrates her victory, however, Twilight frees Cadance, who frees Shining Armor from Chrysalis's spell. Together, Shining Armor and Cadance use their magic to repel Chrysalis and her changeling army. The wedding goes on as scheduled, and Twilight is heralded as a hero by her brother and friends for trusting her instincts.