Marnie Blue is shocked when lots of plastic rubbish starts to appear in Mermaid Lagoon. It's causing all sorts of problems and even harming the underwater animals. Marnie and her friends decide enough is enough and they must have a big green clean-up. But just where is all the plastic coming from? With the help of the local Brinies group, a new dolphin pal and a human friend, the mermaids come …
There’s a new PE teacher at Mermaid School and he’s very strict. Marnie Blue and her friends are horrified when he brings back Golden Glory sports day, with a super-tricky obstacle relay. It’s a turtle disaster! Marnie, Pearl and Orla are put into the same team and get training. But someone has a fishy plot to win all the prizes. Can Marnie stop the cheater from ruining Golden Glory Day?
Marnie Blue has settled into Lady Sealia Foam’s Mermaid School and become best friends with Pearl and Orla. And now might be her chance to shine - the Clamshell Show is coming! Marnie and Orla are both auditioning for the star role, while Pearl (who is no great singer) is sticking to playing the rock tuba. But a new mermaid wins the role, and at rehearsal she's more trouble than a tiger shark…