Sandra (Imelda Staunton) has been married to her husband for forty years. In these long forty years, although it cannot be said that there has never been a dispute between the two, they are also in love. Sandra deeply trusts her husband. However, one day, Sandra was shocked to find that her husband not only had an affair, but the object of the affair was actually her best friend. In sadness and anger, Sandra chose to leave and went to London to join her sister Biff (Celia Imrie). Although they are sisters, Biff's personality is very different from Sandra. Biff is born passionate and cheerful, and is very good at expressing her mood through body language. Sandra decided to go to dance class with Biff. While dancing, Sandra, who had been suppressed for a lifetime, finally found an outlet for her emotions.