When Merliah travels to Australia for a surfing tournament, a jealous competitor steals her mermaid magic and releases the evil Eris from her prison, and Merliah must save the mermaid kingdom without her mermaid powers.
Merliah is an excellent swimmer and surfer, and one day she discovers she can breathe underwater. She meets Zuma, a pink dolphin, who tells her that her mother is the mermaid queen of Oceana.