The midquel of the Elemermaids series and a crossover between the Elemermaids and My Dear Spy. The story focus on Moira, Summer, Hannah, Darby and Loretta teaming up with Sally McNally and her spy friend Ophelia Smith to stop a villainous thief from stealing a magical pearl necklace and taking over the world by turning Waterton into a aquatic doom.

The final story of the Elemermaids series, The girls are now 16-years old, and are getting ready to graduate, everything changes until Charmaine's twin brother, wants to avenge his sister's death by taking over both the world and the sea, and making Moira's friends as his girlfriends, the five girls and their friend Pippa goes to a deserted island, there, they meet Pippa's long-lost twin sister, Felicia.

The Elemermaids meet their new classmate, a japanese-australian girl who dreams of becoming a mermaid, all of a sudden, they discover that Mindy's cousin, Lania, had become a Nure-Onna by a evil Nure-Onna queen and their Nure-Onna folk.

Moira, Summer, Hannah, Darby, Loretta and their close friend Larissa notices the gorgons are turning everybody into one of them, will the girls have to defeat these Monsters?

The Elemermaids enter in a alternative version of their home, where they meet their male counterparts: The evil Elemerboys.

Moira and her friends discovers that their classmate, Charmaine, is a poisonous and dangerous mermaid who poisons anyone in her sight, and they decide to stop her.

Moira, Summer, Hannah, Loretta and Darby's lovely lives are interrupted by a chaotic presence: a group of evil octo-merfolk and their leader.

The sequel of The first Elemermaids book, Moira, Summer, Hannah and Darby goes to a journey to find Loretta, who is captured by a sea eel-like creature.

In the fictional city of Waterton, four high school girls are revealed to be Elemental Mermaids, the ones who will save the world and the sea.