During a scientific experiment conducted by Lewis out at sea, the three mermaids find a wooden statue of a white mermaid on the seafloor! Lewis discovers it's the figurehead of a famous pirate galleon, the White Mermaid, which sank at sea without a trace! Rikki and Emma are thrilled, while Cleo is preoccupied by something else: who is the secret admirer who slipped a heart-shaped shell necklace into her pocket? Our three friends are visited in their dreams by the spirit of the White Mermaid, who demands they find the galleon and bring the wooden statue home. Meanwhile looters are also looking for the sunken ship and its gold, and they'll stop at nothing. Time is running out!