Nelly, forbidden from swimming due to a cold, wishes to be a mermaid and is granted her wish by a Great Seagull. As a mermaid, she befriends Goldfin and Silvertail, but soon finds mermaid life dull and emotionless. Missing her family and human connection, she asks the Great Seagull to turn her back. He agrees, and she wakes up on the beach, realizing the value of her human life and the love of her family after what seemed like a long dream.