Colgate, Lyra, and Carina are confused at why they are selected to be the Brides mares for an alicorn they barely know, Princess Cadance. After being reassured that they are suited for the role they take part in the usual duties of a Bride Mare.
To their surprise they awaken from a trance while falling into a seemingly bottomless abyss.

After spending a year translating an ancient spell, The Great and Powerful Trixie hatches a plan to simultaneously
make herself a hero and humiliate her hated rival, Twilight Sparkle. With Ponyville's first enemies at her side, Trixie is poised to wreak havoc for the Mane 6. Can they overcome their switched flanks, or will Trixie finally fulfill her fondest dreams of revenge?