Miranda is a mermaid with some human DNA in her genetics, since her great-grandfather was human.
One day when Miranda was swimming, she noticed a fisherman, and pulled him underwater. She then took him to his cave with an intent to keep him there forever. The man, Paul Martin, however really wanted to go back to his wife, and Miranda eventually gave in, and agreed to take him back, if Paul would show her around on dry land. Miranda suggested a plan to disguise herself as a woman bound to a wheelchair who is Paul's new patient, obviously having thought on it often.
On land, Paul organized her some clothes and they took a train to London, where Paul let his driver, Charles, to take Miranda to Buckingham Palace, while he went home with a taxi. Miranda complimented Charles often, making him fall in love with her. After arriving to Paul's home, where Miranda was to stay for four weeks, she met Paul's wife, Clare, and they talked for a while. Miranda even tried smoking, but she didn't like it. Miranda spent her night sleeping in the bathtub. The next day Miranda was introduced to Nurse Carey, the only other person who was let on Miranda's secret of being a mermaid. Miranda got her greatest wish to see an opera after Clare organized a visit with her friend and her fiancé, Nigel. Miranda also seduced Nigel and they set up a secret meetings for him to paint her. Miranda was taken to a zoo by Charles once, where Miranda caught a fish meant for a seal, and ate it, she then even talked to a seal, to everyone's surprise. Miranda met with each man privately, she even spent an evening with Paul, swimming in a lake. Miranda gave each men a token of her love in form of a locket with a lock of her hair. During another opera visit with Paul, Miranda took an opportunity to sing. Returning from the opera, Clare hinted that she knows Miranda is a mermaid and compared her with a sea cow. Miranda was very offended by the comparison, and confirmed her suspicions. Miranda then pretended she would allow Clare to see her tail, but once Miranda left the room in the wheelchair, she escaped to the pier, and jumped into the water.
Some time later Miranda had a baby, but it's unknown who the father is. However only Paul knew that Miranda was a mermaid, and both Charles and Nigel affirmed to Clare earlier that they were gentlemanly, and never took a peek of Miranda's legs.
Years later, Miranda spent time in a cave under the Cornwall village with her friend Berengaria. They were heard by Caroline Trewella, a woman who looked exactly like Miranda. Miranda then revealed her heritage, and connection to Trewella family. Miranda saw it as an opportunity to spend some time on land again. Miranda took Caroline's place under pretense that she had an accident and is bound to a wheelchair for a few weeks, while Caroline was on a cycling tour with her friend. Caroline contacted Nurse Carey, to look after Miranda once more. Miranda didn't like Caroline's dresses, so she sold some of her old Spanish coins she had collected and bought new ones. Miranda also disliked Caroline's current fiancé, and was determined to find her a new suitor. As before, everywhere Miranda went, she charmed men. She picked out two who she liked most, an older man, Colonel Barclay Sutton, and a younger man Jeff Saunders. With Barclay, Miranda went to a dinner, and later horseback riding. With Jeff, Miranda did simpler things, like boat rides and fishing. Miranda even gave Jeff a secret fishing location which made him sort of a hero in town for a record catch. Both men wanted to marry her to keep her in town, and Miranda postponed her answer so that it would be Caroline who gives the answer. Miranda also got rid of Caroline's current fiancé when he decided to visit Cornwall and sell the house Caroline inherited there by pouring cold fish soup on him. Barclay's fiancé, Barbara however had found out that Caroline is a mermaid, without knowing that Miranda had taken her place, and planned on revealing it to the world on her concert where she was performing. Fortunately Caroline returned early, and they switched back sooner than planned, with Caroline taking the stage, and Miranda singing under the hall with a microphone. Miranda's singing was interrupted by Berengaria, which made Barbara sprung her trap. When Caroline revealed her legs and danced on the stage, Barbara was humiliated, and Barclay took her home. That left only Jeff as a new suitor to Caroline. Miranda looked over Caroline and Jeff for a while and swam away when she was sure that Caroline and Jeff will be together.