In a hidden underwater city, a young blonde green-tailed mermaid named Maya embarks on an adventure with her beloved doll, Polly. During a visit to the mysterious Blue Holes with her mom, Marni, Maya accidentally drops Polly into one of the bottomless sinkholes. Distraught and unable to retrieve her doll, Maya finds hope when a kind mermaid named Salacia offers to help. Through courage and kindness, Salacia rescues Polly, teaching Maya the power of hope and friendship in the magical depths of the ocean.