It was Thanksgiving eve, 1972. Mimi, the matriarch of the Galvin family, had labored over a flawless meal for her husband and the 11 of her 12 children who had converged for the holiday. If a stranger had glanced inside their home, he or she would have noted a seemingly idyllic scene, punctuated by the gingerbread house Mimi had made and placed on display ahead of what she’d hoped would be a beautiful night. It was not to be. For starters, her eldest son, Donald, picked up the dining room table and threw it at his brother Jim, sending the pressed linen, plates and silver everywhere.

“There may have been no better, more precise manifestation of her deepest fears than this . . . that everything good she had done, all the work, all the attention to detail and love, yes, love, for her family was in pieces.” So relates Robert Kolker, journalist and author of “Hidden Valley Road: Inside the Mind of an American Family,” his nonfiction rendering of how 12 siblings — half of them schizophrenic — and their parents navigated illness, unspeakable violence and the crushed promise of the American Dream.

Kolker’s telling of the Galvin trials is at once deeply compassionate and chilling. He gives as much voice to the schizophrenic siblings — who, one after another, had psychotic breaks, were heavily medicated with debilitating drugs, and were in and out of largely unsuccessful inpatient treatment — as he does to their relatives, many of whom suffered tremendous psychological and sexual abuse from being in their orbit. Interwoven with the harrowing familial story is the history of how the science on schizophrenia has fitfully evolved, from the eras of institutionalization and shock therapy, to the profound disagreements about the cause and origins of the illness, to the search for genetic markers for the disease. Along that path, the Galvins and families like them “continued to live at the mercy of a mental health profession still caught up in a debate that came nowhere close to helping them,” Kolker writes.

The book draws from hundreds of hours of interviews Kolker conducted with the Galvins, their friends and their therapists, as well with the scientists who studied the Galvins’ genetic material to form the foundation for the National Institute of Mental Health’s current research into the genetics of schizophrenia. The latter include Lynn DeLisi, a psychiatrist who, in visiting their home, thought, “This could be the most mentally ill family in America.”

In exploring their story, Kolker finds that, growing up, the healthy Galvin kids were equally tortured by their lineage. “How much longer, they wondered, before it would overtake them, too?” They include the family’s only girls, Margaret and Mary Galvin, each of whom were prey to the brutish roughhousing of their schizophrenic brothers, Donald, Peter, Matthew, Joseph, Jim and Brian. Beyond the bullying, Kolker shares the sisters’ childhood memories of a host of disturbing scenes. Donald looms particularly large initially, as he was the eldest and the first to show signs of the disease.

Mary would come home from school, for example, to find Donald “transplanting every last piece of furniture out of the house and into the backyard, or pouring salt into the aquarium and poisoning all the fish. . . . Sometimes he is sitting in the middle of the living room quietly, completely naked.” Kolker is particularly sensitive in broaching the sisters’ conflicted feelings about their family — what he chronicles as a tortured tangle of hate, guilt and love that they struggled to confront throughout their lives. Despite how traumatic the effects of their illness were for Margaret and Mary, the sisters also recalled the many meaningful attributes of their brothers as individuals: for example, Matthew’s talent as a ceramic artist, Brian’s career as a rock guitarist, Joe’s sense of humor and poignant understanding of his illness.

Kolker, author of “Lost Girls,” about the murders of four sex workers, plies his craft as an investigative journalist and explorer of the less-traveled corners of humanity to individually chronicle the lives of all 14 Galvins. He takes the reader through the family’s history, beginning with the refined Mimi, a daughter of Texas aristocracy who was raised in New York, and her husband, Don, a handsome, all-American military man who taught political science and held domestic diplomatic posts. Between 1945 and 1965, they raised their 10 boys and two girls in Colorado, much of that time in a cul-de-sac on the unpaved Hidden Valley Road.

Mimi had longed for an urbane and intellectual life in the heart of New York City, but her husband’s career took them to Colorado Springs. So she sublimated her dreams into painstakingly creating and molding a perfect family that was initially envied by the community. As the years passed, Mimi became less successful in explaining away the growing chaos in her home that invariably spilled into the streets of her neighborhood. Meanwhile, her husband grew more emotionally and physically remote with each child they had together.

The most complicated character in this story may be Mimi — who is at turns sympathetic and blameworthy. While tending to all of her ill children and doing what she thought was best to keep them out of institutions, she simultaneously avoids even acknowledging their erratic behavior. As Kolker says, from her daughter Mary’s perspective, “To do anything else would be the same as admitting that she lacks any real control over the situation.” Mimi clearly loves her children but is also unyielding in their pursuit of excellence. She is deemed something of a drill sergeant by many of the siblings. Such personality traits led medical professionals of the day to negatively brand her a “schizophrenogenic mother” — a now-discredited theory that so-called domineering mothers were to blame for their children being schizophrenic.

The book gives much space to how difficult the disease has been to diagnose and treat. Yet it ends in 2017, as a story of hope. Kate, one of the Galvin grandchildren, who is interested in neuroscience and schizophrenia, takes a much-coveted undergraduate internship in the University of Colorado laboratory of Robert Freedman. On her first day in the lab, Kolker notes, “she stood near where the data from choline trials on little children were studied for signs of schizophrenia — tests that could change everything for a future generation, thanks to six of her uncles.”

Hidden Valley Road

Inside the Mind of an American Family

By Robert Kolker

Doubleday. 377 pp. $29.95