On Christmas Eve, Agathe von Trapp's great-niece Kirsty disappears from the family gathering. Her father is angry with her for the way she is acting over his remarriage and birth of a new child. It is believed that she has taken the train home to her mother. Agathe is the only one willing to search for Kirsty. She discovers the teenager at the train station. Instead of scolding Kirsty, Agathe mentions that she had wanted to run away herself, long ago. While they wait for the train, she shares stories about her childhood. Agathe led a privileged life as the eldest child of Georg and Agathe von Trapp. The family lived in a beautiful villa in Austria and had many servants. But when Agathe was nine, her mother fell ill and died. Suddenly her world was turned upside down. She was angry at her father for promising that her mother would get well. In protest, Agathe vowed never to sing again. It was a vow she would keep for ten years. The family moved to Salzburg to make a fresh start. Agathe was heartbroken at leaving her playmate Sigy, grandson of the housekeeper. As she grew older she took charge of the house, the servants, and her siblings. Captain von Trapp hired a succession of nannies but Agathe found fault with each one. Then her father hired a novice nun called Maria, who was young and very attractive. Right away there were problems. Agathe didn't welcome Maria but was relieved to learn that she was only to be there for a few months. Captain von Trapp urged Agathe to get out and make friends, go to concerts, and have some fun. But Agathe wasn't interested. She was delighted when her old friend Sigy moved to Salzburg to work as an apprentice printer. Captain von Trapp hires a chauffeur, a man named Conrad who had served under him in World War I. While Conrad appears grateful, it is obvious that he isn't happy accepting charity. The inevitable happens when the captain and Maria announce their engagement. He asks Agathe for her blessing which she is unable to give. At the wedding she finds it difficult to act happy. Maria eventually gives birth to her own children, which further antagonizes Agathe. She spends a lot of time with Sigy, who tells her that great changes are coming to Austria. Sigy and Conrad have a similar discussion and Agathe learns that Conrad is a Nazi. The family is plunged into poverty when the bank containing Captain von Trapp's money fails. Maria asked what they will do now but her husband doesn't want to think about it. It is obvious that Sigy is in love with Agathe, but he is too shy to tell her. Agathe only sees him as a friend anyway. She is worried when Sigy joins a group of rebels. At night, they travel through Salzburg defacing posters of Hitler. Many people are leaving Salzburg but the captain won't consider it. Since the family can no longer afford servants, Maria insists they be discharged. Conrad doesn't take this well. He argues with Captain von Trapp but to no avail. The Salzburg music festival is approaching but tickets are sold out. Agathe longs to hear her singing idol, Lotte Lehman. Sigy sneaks her into a rehearsal but they are discovered. Lotte takes pity on Agathe and on learning that she hasn't sung for ten years, invites her onto the stage. Reluctantly Agathe sings a piece by Schubert. Her voice is thin but improves when she starts to relax. Lotte compliments her and Agatha leaves happy. Sigy and his group are caught and he is severely beaten, dying on the way to the hospital. Agathe is heartbroken. When she visits his grandmother, she learns of his love for her. At this point Kirsty interrupts to ask if that is the reason Agathe never married. Agathe avoids giving a direct answer but says that she never met anyone else like Sigy. Lotte Lehman stops by and asks the von Trapp children to sing for her. She then asks them to not only participate in the music festival but to accompany her to America, where they can open for her. When Captain von Trapp learns that Agathe had a hand in this, he angrily confronts her. They quarrel and he orders her to leave. While the family is at dinner, she packs up and heads for a nearby bus stop. To her surprise she is joined by Maria. They embrace and Maria suggests they go to church and light a candle for Agathe's mother. For the first time they agree on something; that the family must sing at the festival. Since the captain has forbidden it, Maria says they must come up with a solution whereby he will think it is his idea for them to sing. Conrad pays a call on Captain von Trapp and brings him a Nazi flag. He hints that if the captain's anti-Nazi views become known, he and his family could lose their home. The captain angrily orders him to leave and throws the flag away. The night of the festival arrives and the von Trapp children prepare to leave. Their father initially refuses to accompany them but once they are on stage, he shows up and joins them. Conrad and his henchmen view this as a direct insult to the Nazi's. The next day he delivers an ultimatum. The captain is offered a place in the German navy. If he doesn't accept it, he and his family will be in serious trouble. The deadline is that night. The family immediately begins packing. It is their plan to cross the border and go to America. Just in time they escape out the back door as the Nazi's storm the house. They trash the house, stealing many antiques and breaking things. The von Trapps hear the sound of breaking glass as they hurry away. Here Agathe's story ends. Kirsty decides she was wrong to hate her stepmother and decides to return. Her father is more than ready for a reconciliation. Viewers learn that the von Trapps had a long and successful career, performing to audiences world-wide for many years.