Echo loves dancing in the Trident Academy Tail Flippers. When she's not dancing, she also loves riding sea horses, so when a classmate offers to let her ride their newest horse, Pinky, she doesn't think twice!

But when a slithery eel darts in front of Pinky, Echo gets knocked off and hits a rock. Her entire body aches--from scales to tail--so she heads to the doctor. Dr. Weedy tells Echo that moving her tail is absolutely out of the question. Not only can Echo not swim, but even worse, she can't compete in the Poseidon Tail Flippers team competition! And Echo's their star flipper. Without Echo's tricks and flips, Trident City's team doesn't stand a chance.

Echo's friends find a pair of human crutches, which help her get around without the use of her tail. But that doesn't solve the Tail Flipping problem! Will Echo find a way to help her team win from the sidelines?