It is Shyanna's long-awaited, all-important thirteenth birthday, but nothing is going right--and when Cora's baby sister Jewel gets trapped in a fishing net, Shyanna is the only one small enough to get inside the net and rescue her at the risk of being turned into a human forever.
Rachel is new to the Kingdom of Neptunia, and she has two secrets--she is half human which only her friend Shyanna knows, and her boy friend is a human boy, Owen, who does not know know she is a mermaid.
The Spirit Squads that represent the different castles are an important part of the Kingdom of Neptunia, and Cora and Shyanna are delighted to be chosen--but their friend Rachel was left out, and when Cora finds out why, she is forced to make a big decision.