Despite what the songs say, everything is not better under the sea! The flowers are leaking green ooze, the food is filled with sand, and the coral is dying. The water is growing more treacherous, and it's up to the newly seapony-fied Mane Six and their ragtag group of pirates (and princesses) to get to the bottom of things, even if that means exploring the dark trenches everypony fears. The barnacle-covered truth of the Sparkling Sea is soon to be revealed.