The following version of the book was used to create this study guide: Kolker, Robert. Hidden Valley Road: Inside the Mind of an American Family. Toronto: Random House Canada, 2020.

Mimi and Don Galvin married in 1944, just before Don went overseas to serve with the navy. From 1945 to 1965, they would go on to have twelve children: ten boys followed by two girls. Don's career in the military would lead them to settle in Colorado where he worked with the Air Force. In this mid-century period, schizophrenia was not well understood. Researchers, scientists, and psychotherapists were divided over its causes and treatments, and the nature versus nurture debate raged. As teenagers, the two eldest Galvin boys, Donald and Jim, developed a strong rivalry. There were many fights in the home between all the brothers, which Don and Mimi dismissed as boyish rowdiness.

The eldest, Donald, began showing signs of psychosis while in college. Ill-equipped medically, financially, and psychologically to deal with their son's issues, Don and Mimi hoped they would resolve themselves. Donald's condition continued to deteriorate over the years, however, to the point where he tried to murder his wife and kill himself. His attempt failed and he soon fell into a cycle of circulating between living at home with his parents and being committed to state hospitals. This cycle would last decades and Donald's presence in the family home would come to be a source of violence, tension, and fear, particularly for his younger siblings. Meanwhile, the second son Jim married and had a son of his own before his wife, with whom he was physically abusive, began to notice that he was also showing signs of mental illness. He agreed to counseling and medication and appeared to stabilize.

To escape their unhappy and tumultuous home life, the youngest Galvin children, Margaret and Mary, would often spend weekends with Jim's family. On these visits, they were frequently sexually molested by their brother, but told no one. In the late 1960s, researchers were beginning to find evidence that biology (i.e., nature) plays a significant role in the development of schizophrenia. This was the beginning of a major shift in the debates about schizophrenia as well as in our collective understanding of the illness. In 1973, the fourth Galvin child, Brian, who had moved out to California, shot and killed his ex-girlfriend and himself in a murder-suicide. What his parents had known but not told anyone was that he was taking antipsychotics before his death. In 1975, Don suffered a stroke that severely compromised his health, and the youngest son, Peter, had a psychotic break. With the home situation deteriorating more and more, the decision was made that Margaret, the eldest of the two Galvin girls, would go and live with wealthy family friends, Sam and Nancy Gary.

In the second half of the 1970s, researchers began looking at families in order to study the potential genetic components of schizophrenia. Matt also developed schizophrenia in this period. There were now three mentally ill boys living at home in between their bouts of hospitalization, Donald, Peter, and Matt. Their sporadic outbursts and increasing violence made home-life difficult for Mary. At thirteen, Mary stood up against Jim. He raped her, but then never touched her again. Not long after, Mary was gang-raped at a party. She succeeded in arranging a place for herself at a boarding school, funding in part by scholarships and in part by the Garys, and moved away from her family to attend high school on the east coast. At orientation, she changed her name to Lindsay.

In 1982, the seventh son, Joe, had a psychotic break. Lindsay began seeing a therapist to work through her many traumas, which was a long but ultimately productive process. She also began thinking about what types of treatments were available to her brothers. She told her parents about Jim's abuse and he was banned from their home. In 1984, the Galvin family began participating in a research study on the genetics of schizophrenia. The healthy members of the family continued to move forward with their lives, while the sick ones continued to struggle. Margaret also eventually sought therapy and embarked on a healing journey. Lindsay tried to offer Peter better care and quality of life by taking him into her home but ultimately there was nothing she could do to keep him healthy and stable long-term. Mimi, in her advancing age, continued to care for her ill sons who were still living at home as well as her husband whose health was in severe decline.

Research into schizophrenia continued into the 1990s and 2000s with an increasing focus on genetics and biology as the physical components of the condition became more and more clear. Despite various advances that helped improve our understanding of the illness, few advancements were made in terms of treatment options. The medications available continued to come with negative physical side effects that were, in some cases, as bad as the disease they were intended to treat. Research then began to focus on the possibility of preventing schizophrenia before it develops. In the 2000s, Jim and Joe both died of heart conditions that were attributed as side effects of their neuroleptic drugs. Don Galvin died of cancer in 2003 at 78 years old. As Mimi aged, her sons no longer lived with her, primarily moving to assisted living facilities.

In her early nineties, Mimi's health decline severely subsequent to a stroke. Lindsay and Michael were the only healthy Galvin siblings to take on caregiving roles as most other healthy members of the family had no ago distanced themselves. Mimi died in 2017 and the surviving Galvin siblings reunited for her funeral, though Margaret and Richard were notably absent from a sibling dinner. Over the years, Lindsay has had to recognize and accept that her siblings do not take on a caregiving role with their ill brothers as she does. She is now their primary advocate and caregiver but with her gentle prodding, some of her well siblings are beginning to reach out to the ill ones.

At the end of the book, readers are asked to think about how the lives of the sick Galvin boys might have turned out differently if they had been born in a different time, if a better understanding of the illness had existed, or if there had been better treatment options available. Looking to the next generation, Lindsay was able to provide therapeutic resources for her children as they were growing up, and she wonders how her brothers' lives might have been different if they had had these same opportunities and resources.