In this enchanting tale, best friends Charlotte and Mia are delighted to meet the mermaids who live in the lagoon at Wishing Star Palace. However, their joy is short-lived as the lagoon turns a murky, toxic green. The mischievous Princess Poison is at it again, casting an evil curse. To break the curse, Charlotte and Mia must grant four more wishes. One of these wishes comes from Freya, who hopes to find buried treasure on her family's treasure hunt. Can Charlotte and Mia solve the mermaid mystery and grant Freya's wish?