Welcome to Lady Sealia Foam’s Mermaid School! Here you will learn siren songs, proper care of sea creatures and how to not fall off your seahorse

Marnie Blue and her friends are horrified to discover they have a new P.E. teacher at Mermaid School, and he's very keen to improve everyone's fitness. Worse, he's bringing back the Golden Glory sports day. It's a turtle disaster! Marnie, Pearl and Orla are put into the same team to compete in ultra fishball, the obstacle relay and the seahorse riding events. But someone has a fishy plot to win all the prizes. Can Marnie stop the cheater from ruining Golden Glory Day?