The heroine of the novel, Mina, the only daughter of Madame de Fontaine, is in love with Fritz. But Fritz's father is opposed to his son's marriage and believes that Mina and her mother encroached on the family's wealth. Suddenly, the groom's father, Mr. Koehler, falls ill, and Madame de Fontaine gives the sick man a miraculous medicine. She cures him of a fatal illness. But this medicine turns out to be an antidote. Who poisoned Herr Koehler?