"We all make choices. But, in the end, our choices make us."
-Andrew Ryan

After her adventure in the "mirror world", Princess Twilight is ready to settle down in her home in Ponyville. She and her friends prepare for the passing of Astra's Comet, a celestial body that increases the magical powers of every unicorn in Equestria. But, as the comet passes, Twilight uses her new found alicorn powers and opens a portal to another world. Out of this portal, metal giants, called "Big Daddies", emerge and attack the residents of Ponyville! During the chaos, Twilight is knocked into the portal and transported to a world where one man, Andrew Ryan, has built the impossible: the underwater city of Rapture.
While exploring the soaring heights of Rapture, Twilight encounters many enigmatic characters and uncovers dark secrets that will, forever, change her life.
The question is: will her choices affect those around her and will they be her undoing?