Meet Isadora Moon's mermaid friend, Emerald! Emerald is learning how to be a mermaid princess, but there are just so many rules. She loves having fun with her friends and exploring her underwater world with her pet octopus, Inkibelle, she doesn't want to be stuck in the palace with everyone looking at her and checking that she's doing things the proper, royal way. Emerald's mum and stepdad King Auster are busy preparing for a very important visit from another royal family-The Seadragons!Emerald is on her best 'princess-like' behaviour even though she'd much rather be wearing her comfy clothes, hanging out with her friends and pet Octopus, Inkibelle.

When Prince Mola Seadragon takes a Manta Ray from the royal stable and runs away, Emerald follows. On an adventure across Scallop City, Emerald and Mola discover they have much more in common than they thought.