Sofia and her family are exploring marrowy cove on their floating palace. Its a holiday fit for a princess, and it gets even better when Sofia meets a mermaid named ozone. But then ozone is kidnapped by a hideous sea monster and the mermaid queen thinks the humans are to blame! Sofia doesn't know what to do, but a few loyal friends and a very special visitor might be able to help her work out how to swim to the rescue.