The novel revolves around the lives of the Lambert family, an old-fashioned midwestern couple and their three adult children. The parents, Alfred and Enid, are dealing with Alfred's Parkinson's disease and their own marital problems, while their children are each facing their own personal and professional crises. The narrative explores the themes of family dynamics, societal expectations, and the struggles of modern life. The story climaxes with the family's last Christmas together at their childhood home.

The book follows the life of a former high school basketball star, who is now in his mid-forties and has inherited a Toyota dealership from his father-in-law. He is living a comfortable life with his wife and son in Brewer, Pennsylvania during the late 1970s. The story unfolds as he navigates through his midlife crisis, dealing with his rebellious son, his longing for his old mistress, and his own insecurities and dissatisfaction. The narrative provides a deep dive into the protagonist's thoughts and feelings, offering a detailed examination of middle-class American life during this era.

The novel follows the life of a 39-year-old single, childfree woman living in New York City who is dealing with the societal pressures and expectations of adulthood. Her journey is marked by her struggle to find happiness and fulfillment in her own terms, despite her unconventional lifestyle. The protagonist grapples with her relationships, career, and the looming presence of her family's tragedies, all while trying to understand what it truly means to be "all grown up".