An American woman marries a German professor, who gains citizenship but cannot overcome hatred of Germans during the World War.
In 1909 Sam Archer (Frank Albertson) makes fun of Germans while his sister Mary Archer (Barbara Stanwyck) prepares flowers. Jeff (Ralph Bellamy) arrives from Germany with Hugo Wilbrandt (Otto Kruger), who kisses her hand. Hugo sings German love lyrics to Mary and translates. Sam is angry that Mary is going to marry a German. Hugo teaches chemistry, and Mary cooks. Mary and Hugo buy a puppy, and Mary has a baby. Hugo renounces Germany and swears loyalty to the United States. At a party they sing patriotic songs, and Hugo is given a cup commemorating his citizenship. That day Germany invaded Belgium.
In 1915 German torpedoes sink the Lusitania, and angry Sam comes to Mary for his things. No one attends her tea. Hugo learns he lost his job but refuses to go to Mary's parents. Their son Teddy (Ronnie Cosby) is sick, and Hugo sings to him until he dies. Kids kick the German dog Anna (Clara Blandick) walks. Hugo tells Mary he may have a job. Anna says that kids threw rocks at their dog. Hugo finds the dying dog and shoots it. Grandma Archer (Laura Hope Crews) and Jeff come for Mary and Hugo, offering him a job. He accepts; but when he refuses to change his name, Mary collapses. Hugo tells Mary to go and says he will come next week. They say good-bye.
Mary's cousins turn off "Silent Night" because it is German. She gets a letter from Hugo that he can't be an American and so will go fight for his people. In November 1917 Mary in uniform says she got her divorce. Mary comes back, and Jeff in uniform greets her in the garden. They agree they are made for each other.
In France Mary welcomes two women and takes a gun and poison away. Jeff visits Mary. In a canteen Lefty tells Mary about a big troop movement. Mary sees Hugo in uniform and distracts Jeff, who says a spy is loose. Mary finds Hugo hiding in her room and says she won't help him. They embrace and kiss. At 4:45 a.m. Hugo says he has a chance now. They see men marching. Mary puts poison in both wine glasses. Hugo drinks first, but she drinks too. Slowly he dies, and then she does too.
This melodrama explores the hatred of Germans caused by war hysteria in America. Treated like an enemy, Hugo finally acts like one.