Mr. Peabody and the Mermaid is based on the novel of the same name by Guy Pearce Jones and Constance Bridges Jones. Underwater part of the movie was filmed in the Weeki Wachee Springs.
Mrs. Polly Peabody seeks help from a psychiatrist about her husband Mr. Arthur Peabody, about the mermaid he caught in the Caribbean while fishing. Dr. Harvey then wanted the hear the story from Mr. Peabody himself. Mr. Peabody then proceeded to tell the events that happened on St. Hilda's.
Mr. Peabody was a bit ill, and was on a vacation, recovering. On his first day, Arthur heard a lovely singing. At the beach party Arthur looked for a singer, Cathy Livingston, who he thought he heard earlier, but when he heard her singing, he didn't recognize the voice. The next day while on fishing, he caught a mermaid. He took her back to the hotel, and planned on sending her to American Museum of Natural History. Polly came home and saw the mermaid's tail in her bath, thinking it to be a regular fish, she ordered her husband to get rid of it. Arthur took her out, planning to return her to ocean, but then rethought his plan. He sat near the hotel's fish pool to rest. Arthur named the mermaid Lenore, and professed his love to her. Lenore fell into the pool. The next day he went and bought several bathing-suits for Lenore, to make her more presentable. Cathy Livingston was chasing Arthur, one day near the fish pool, she asked Arthur to bring her a drink, and then jumped into the pool. Lenore grabbed a hold of Cathy and bit her leg. Polly grew jealous and wanted Arthur to stop seeing Cathy, who she though he was having an affair. Arthur promised to do so, knowing that nothing happened between the two of them. Arthur sneaked out to be with Lenore, and Polly saw them. She stormed out in the middle of the night. Arthur was happy that he got to spend time with Lenore. But after several weeks, people started to notice, that Polly has disappeared. The police got involved, thinking that Arthur had killed his wife. Arthur escaped with Lenore to the Cay, but the police found him. They informed Arthur that Polly was found, and that she had returned to Boston. The men all heard Lenore sing, and Arthur jumped into the water to be with her. He sank, and Lenore came to him, dragging him to the bottom.
At the present: Dr. Harvey urged Arthur not to tell people that story as they wouldn't understand, as it wasn't anything more than a midlife crisis, and told his own story of a figure skater he supposedly met. Arthur went home to his wife, and told that the mermaid wasn't real, and that the doctor was sure he was hallucinating. Arthur then gave Polly a gift, one of Lenore's hairpins.