Twilight is an academician, and the renown student of Princess Celestia.
After a diplomatic visit to the Arabian University of Magic on the behalf of her mentor, she's ready to enjoy the trip back to Equestria on one of the most luxurious steamers crossing the seas, whereas a certain Princess of the Night is hitching a ride onboard, looking for a dangerous and dark-magic inclined artifact.
When those two meet, things start falling apart.