Thora - half-mermaid, half-human - sails to London with her mermaid mother, Cosmo the peacock, and her newest friend, Shirley the sea horse. P. Poutine - a mermaid Cruella de Vil. Pamela will steal anything she can - including Shirley, who's a rare and priceless green dragon sea horse. And when Pamela finds out that Thora has the legendary projectionist's ring, she'll stop at nothing to get her hands on it ...