Erika a young girl walking along a deserted beach finds aninjured and dying mermaid carries her home and nurses herback to health. Once her body is whole again Maari the mermaidis able to turn herself into a human girl. When she gets homesickErika and her Dad take her home to the island of Tiki-roa.Several years later Erika returns to Tiki-roa. They often play atthe girls secret lagoon in a cave of the ancient Maoris and onSkull Mountain where they encounter a huge flightless moa birdand find a cave with pirates treasure of pearls.At the end of her stay Erika meets Maaris mother the mermaidCyrena and her father Jupiter mighty ruler of all the oceans. Ingratitude for saving their daughters life they bestow upon Erikathe power to turn herself into a mermaid.