What if Ariel had never defeated Ursula? It's been five years since the infamous sea witch defeated the little mermaid ... and took King Triton's life in the process. Ariel is now the voiceless queen of Atlantica, while Ursula runs Prince Eric's kingdom on land. But when Ariel discovers that her father might still be alive, she finds herself returning to a world--and a prince--she never imagined she would see again.--

Ven, Char, and the merrow Amariel explore the world beneath the sea, where beauty is more than matched by dangers, and soon they realize that in order to save thousands of innocent lives, they may have to sacrifice their own.

"As the mermaid Crown Princess of Thalassinia, Lily must dive deep into findng a solution when she discovers the ocean's warming is causing big waves for both mermaids and humans"--

As they search for their missing father near their Cornwall home, Sapphy and her brother Conor learn about their family's connection to the domains of air and water.

Two years after the disappearance of their father, Sapphire and Conor, having moved with their mother to the town of St. Pirans, try to make a new life for themselves, but Sapphire, unlike her mother and brother, finds it increasingly difficult to adjust to her new circumstances and is drawn more and more to the undersea world of Ingo.

When the ferocious shape-shifting Kraken awakes after thousands of years and threatens the Mer, Sapphire agrees to help them by going with her brother Conor and their friend Faro into the Deep to lull the monster back to sleep.