It's summer, and the mermaids have trained their tails off at Hillnook Lake. Prepared for a vacation full of fun (and maybe a little mermaid work) they set off for East Hillnook. But when they arrive... Tourists have horribly littered Starfish Hill. And what's worse, garbage is floating out to sea in droves, where sea turtles are eating it...instead of jellyfish! Now, it is up to Monica and a beautiful, but deemed "useless" trident, to save the day. Only problem is, none of the other mermaids believe in her plan! Can Monica trust her gut to save the turtles?