Mary Archer expects to marry her cousin Jeff when he comes home from studying in Europe in 1909, but when she meets his German friend, Hugo Wilbrandt, she falls hopelessly in love. Despite her family's opposition, the two are married and Hugo takes a position as a college professor. They are extremely happy and grow closer with the birth of a baby boy, after which, Hugo proudly becomes a United States citizen. When the war breaks out, however, Hugo is snubbed by the community and dismissed from his position because of anti-German sentiment. After their child dies, some neighborhood kids stone the boy's dachshund nearly to death, and Hugo, taking pity on his beloved pet, fires a bullet into the dog. When Mary's grandmother offers Hugo a job in the family mill if he will change his Germanic name, he refuses, saying he is not ashamed of it. After Mary becomes ill, Hugo sends her to live with her family and leaves for Germany, saying he will return. However, Mary later gets a letter in which Hugo writes, "They let me be a citizen, but they won't let me be an American," and announces that he is going to fight for his people. Mary divorces Hugo and plans to marry Jeff, who joins the army and is sent to France. Mary follows him and goes to work in a canteen. There, she sees Hugo dressed as an American soldier and learns from Jeff that a German spy is in the area. That night, Hugo meets Mary in her room and she realizes that she is still deeply in love with him. Certain that he is the spy, she must choose between her own feelings and her duty to her country. He spends the night with her, and as dawn breaks, she poisons their wine and they die together.