Johannes Wolfgang and his wife live in abject poverty. A violin-builder, he toils from dawn to dusk, assisted by his aging father, but still the business is not profitable and he falls deeper into debt with his suppliers. One day, a message from one of them informs him that he should not expect to receive more supplies until he pays what he owes. In despair, he calls on his good friend, the impresario Kurt Rosegger, who has helped him out before. Rosegger, for his part, has just received a letter from his cousin, the virtuoso violinist Kai Rosegger, regarding a tour of the provinces. Enclosed with the letter is the sum of 300 crowns to cover expenses. This is all the cash Kurt Rosegger has when his friend Wolfgang comes asking for a handout. Wolfgang’s tale of woe – his wife is deathly ill in bed – touches Rosegger’s heart and he offers to tide his friend over. Grateful, Johannes swears to repay Wolfgang on time. Three months later, Kai Rosegger has abandoned his tour and sends an impatient letter to Kurt, threatening to go to the police unless he gets his money back immediately. Kurt Rosegger forwards the letter to Wolfgang, who despairs and chooses to take his own life rather than live in dishonour.
The letter, signed K. Rosegger, is stuck into a half-finished violin and when it is discovered, the family harshly, but unfairly, blames Kurt, not Kai, Rosegger. Wolfgang’s widow is so distraught that she succumbs to her illness a few days later. On her deathbed, she makes her father-in-law swear to tell her son, Richard, when he has grown up, everything that has happened in the last few days. "Teach him to hate the man who killed his parents," she says.
Nearly 25 years later, Richard is now a famous musician and the impresario Kurt Rosegger has become a wealthy man, whose only joy in life is his daughter Else, a lovely girl of 20. Richard has become quite infatuated with the young lady. He proposes to her and she accepts. A few days later, when Richard turns 25, he gets a visit from his grandfather. Richard nearly goes mad with grief when he learns that his fiancée’s father is the man who killed his parents. His grandfather makes him swear to destroy the beautiful violin he got from his father if he ever breaks his vow to avenge his parents. The next day Richard has a heart-to-heart talk with Else, demanding that she choose between him and her father. She chooses the man she loves and soon they marry.
A year and a half has passed since father and daughter were estranged. Kurt Rosegger is at a loss to explain this unhappy state of affairs, but for fear of wrecking his daughter’s happiness he has not demanded an explanation. As a small consolation, the nursemaid has been taking his infant grandchild to the park every day. When the nursemaid and the child fail to appear for several days in a row, old Rosegger gets anxious. He rushes to his daughter’s house and gets hold of the nursemaid who tells him the child has fallen ill. Hearing that her father is showing concern for the child, Else’s heart melts and she allows him to see his grandchild. When Richard comes home, she hides her father, who listens in as the doctor tells the young parents that their child’s illness is life-threatening. Unless surgery is performed, the child will die. Unable to restrain himself, Rosegger bursts out and puts down the 500-600 crowns they need for the operation. Realising he has broken his vow of vengeance, Richard takes his father’s violin and smashes it over his knee. A yellowed piece of paper falls out of the violin – it is Kurt Rosegger’s letter to Johannes Wolfgang. All doubts and misunderstandings among the three family members are dispelled and they unite in joy at the baby.