The setting is Germany in the late 1920s. Rosalie, the central character, is a "sociable," cheerful 50 year old widow who lives with her adult unmarried daughter and her adolescent son. Her manner is youthful but "her health had been affected by certain critical organic phenomena of her time of life." Rosalie is keenly aware of all that menopause implies: the loss of sexual allure and of a (biologic) purpose in life. She feels "superannuated."

Along comes a young man, well-built, who is the American-born tutor for her son. She is overwhelmed by physical attraction for him, becoming infatuated, much to the disapproval of her repressed, cerebral daughter. She feels young and attractive once more, believing that her heightened state of sensuality has resulted in the resumption of what appears to be menstrual bleeding.

Planning to declare her love to the tutor, Rosalie arranges a family excursion to the Rhine castle where the black swans swim. In the decaying alcoves of the castle, she does so; the pair will rendezvous that night. The rendezvous never takes place; Rosalie has hemorrhaged. She is found to have a large, metastatic uterine tumor.