Jeannette Walls was born on April 21, 1960, as the second child of Rex Walls, a former Air Force pilot and an engineering prodigy who struggled with alcoholism; and Rose Mary Walls, a passionate artist who suffered from frequent flights of fancy and radical mood swings. She was raised alongside her older sister Lori, her younger brother Brian, and her younger sister Maureen.
Jeannette's first memory is of an ill-fated attempt to boil hot dogs at the age of three that ended in her dress catching fire, leaving burn scars on her abdomen. While staying at the hospital, enjoying a comfortable bed and plentiful food while doctors and social workers investigated her home situation, her father Rex comes to pick her up and "skedaddle", escaping from town in the family car: this was a frequent occurrence for the Walls family whenever debts or local authorities threatened their way of life.
The Walls family would often "skedaddle" throughout the American southwest, with Rex sharing ideas with Jeannette, whom he affectionately nicknamed "Mountain Goat", about a "glass castle", a self-sustaining solar-powered homestead where they would live once they had the land and resources to build it.
When Jeannette was 7, she and her family moved into Battle Mountain, Nevada, living out of a re-purposed train station while Rex worked in the mines. For the first time in a long time, the family enjoys some stability as the work Rex does makes just enough money for them to afford food and shelter, but not enough for him to spend on alcohol. Sadly, the stability would not last; six months after arriving, Rex loses his job in the mines, and the family falls into poverty. Rose Mary pursues a job in education to keep the family from starving, but life proves hard for Jeannette when a kid that moves into town, Billy Deel, takes a liking to her and tries to force himself on her. When Jeannette rebuffs his advances, Billy retaliates by firing on her and her siblings with a BB gun. Jeannette and Lori scare Billy off by firing warning shots at him using their father's pistol. This attracts attention to the family from authorities, prompting Rex to pack up the family and leave Battle Mountain in the night.
The Walls family makes their way to Phoenix, AZ, where Rose Mary's mother lives. Rose Mary hopes to be able to introduce the kids to their maternal grandmother, but when they arrive, they find that she had already passed away. Thankfully, her house and a sizable inheritence was willed to Rose Mary, so the family moves in. The family enjoys some stability again, but things begin to seem amiss when Rex and Rose Mary insist on leaving the doors and windows open at all times. This causes a stranger to wonder into the house and molest Jeannette, who is thankfully rescued by Brian, who brandishes a hatchet to chase to pervert away.
Rex, who isn't pleased with living in a big city like Phoenix, continues to struggle with maintaining employment, which causes his alcoholism to worsen. For her 10th birthday, Jeannette asks her father to stop drinking. Rex ties himself to a bed to keep himself from drinking and fight through the detoxing process and succeeds in kicking the habit, but suffers a relapse during an ill-fated attempt at a trip to the Grand Canyon.
Money becomes so scarce that, in spite of Rex's protests, the family is left with no choice but to move to Rex's hometown of Welch, WV, where they can get support from Rex's parents. Life in Welch is less than ideal; the town being heavily impoverished, Jeannette's paternal grandmother Erma is harsh on the house guests, and the children are enrolled in special education classes when they are mistaken for slow due to their accents.
When Rex and Rose Mary leave the children in Erma's care while they returned to Phoenix to retrieve their belongings, Jeannette witnesses Erma sexually abusing Brian. This escalates into a physical confrontation between Lori and Erma that ends with them confined to the basement for the duration of Rex's trip to Phoenix and, afterwards, the family moving out, leaving Jeannette to wonder if Erma abused Rex, thus explaining his protests against returning to Welch.
The family uses some of their remaining money to move into an old house without plumbing or electricity, in the poorest neighborhood in town. The children's spirits are lifted when Rex declares the land around the house the best place to break ground on their glass castle, but spirits come falling down once more when the land they dig up to make the castle's foundation is used as a trash dump due to the family being unable to afford garbage service.
As time passes, Rex is home less and less often. When he does come home, he is often drunk and injured. His continued inability to hold down a job leaves the children hungry often, forcing them to do what they could to feed themselves, either foraging for berries or digging through garbage. Winter also leaves them cold, due to their inability to use the coal stove for a lack of coal.
After Erma passes away, Jeannette's grandfather and uncle move into an apartment following their home burning down. The family visits them for warmth, laundry, and baths; but Jeannette's uncle molests her during one of their visits, prompting her to stay home when the rest of the family went and leaving her to try to bathe herself as best as she was able.
When Jeannette starts attending high school, she takes to participating in making the school newspaper. Her work on the school paper gives her access to the Associated Press wire, which gives her news from around the world that shakes the worldview her parents had instilled in her with their unorthodox parenting methods. This, combined with their living conditions in Welch, causes her to begin to realize that her life was a far way away from normal...
Rose Mary had taken on work as a teacher to try and put food on the table, but her job leaves her suffering frequent mental breakdowns. Jeannette convinces her to go to teacher training for a few weeks, and Rose Mary leaves two hundred dollars for groceries before she leaves. This money, however, evaporates quickly when Rex uses much of it to drink. He promises to pay her back, and to that end, enlists her aid in a pool hustling scam where he wants Jeannette to use her good looks to make his opponent lose. As part of the scheme, Rex has Jeannette accompany his opponent upstairs after playing, where he attempts to sleep with her. Jeannette is able to repulse him by showing him her burn scars, and refuses to take her cut of the hustle money from Rex.
When Rose Mary returns, she refuses to get a new teaching job, leaving the children hungry again. When Rex whips Lori, who had attended summer camp for gifted students, at Rose Mary's request for calling her out on her selfishness, Lori concocts a plan: she wants to leave Welch as soon as humanly possible, and begins to save every cent she can to fund her departure. She plots with Jeannette to move to New York City after graduating, with Jeannette joining her the following year when she graduates. Together, they would make enough money to help Brian and Maureen join them.
The plan is nearly derailed when Rex steals money from a piggy bank that Lori used to save for her escape, but she manages to find her way out when a family Jeannette babysits for suggests taking her on a trip to Iowa. Jeannette asks them to take Lori to New York instead and thus, Lori manages to escape from Welch.
Jeannette becomes the editor-in-chief of the school newspaper by her junior year, and begins to consider going to college in New York after graduating, only to learn that tuition would be more expensive as an out-of-state student. She plots instead to move before starting her senior year so she could be considered an in-state student and thus have lower tuition. Rex, heartbroken after Lori's departure and dreading the prospect of his beloved "Mountain Goat" leaving him as well, tries to convince her to stay so they can build the glass castle. Jeannette has realized by now, however, that the glass castle is nothing more than a pipe dream, a fantasy that could never come true. Rex reluctantly accompanies Jeannette to the bus station and sees her off as she leaves Welch, her parents, and her hectic past behind.
Jeannette moves into a hostel in Bronx with Lori and works at a hamburger shop before getting an internship for a small newspaper, The Phoenix, after graduating. She learns from phone calls with Brian that life in Welch is getting worse; Rex is either drunk or in jail, and Rose Mary took a nasty fall off their house's dilapidated porch. Brian immediately moves to New York with Maureen as soon as he is able, finally reuniting the Walls children in New York, enjoying lasting financial and emotional stability at long last.
Their past, however, catches up with them when Rex and Rose Mary move to New York to be with their children. Their inability to afford rent sees them moving in with Lori and Brian for a time, but Brian's strict rule against alcohol and Lori being unable to deal with Rose Mary's habitual hoarding sees the two parents living on the streets. Jeannette considers dropping out of college so she can look after Rex and Rose Mary, but Lori and Brian convince her to continue to pursue her education, because their parents are dead-set in their ways and couldn't really be helped. Rex gets clean again while staying in the hospital to be treated for tuberculosis, but relapses again, his drinking partially fueled by guilt over his inability to provide for his family. Nonetheless, when Jeannette faces the prospect of dropping out when she can't afford tuition, Rex manages to provide her with enough money to pay for her education from gambling.
Eventually, Rex and Rose Mary take to squatting in an abandoned building, leaving Jeannette with a small sense of relief as her parents finally find their place in the world among like-minded squatters.
After graduating from college, Jeannette finds work for a major magazine, becoming financially independent and finding a relationship with Eric, a young man who is the opposite of her father in every conceivable way. When Rose Mary visits her home one day, she asks if Jeannette is really happy, a question that is hard for Jeannette to answer; she enjoys her life among the upper crust of New York society, but finds herself hiding the truth about her upbringing from her peers, fearful that it would cost her her job and status. Eventually, she learns from Rose Mary that an uncle of theirs, Rose Mary's brother, died, and she needed money to buy his land holdings in Texas that were worth over a million dollars. Jeannette is left incensed at their mother's refusal to use that land to provide for them growing up.
In time, the elder Walls children find success and happiness of their own; Brian becomes a police officer while Lori becomes an illustrator, as Jeannette, herself, becomes a successful writer. Maureen, sadly, becomes a drifter who stays with her parents until she stabs her mother, resulting in her being sentenced to a psychiatric facility. An argument over whether their parents were at fault for what befell Maureen causes Jeannette, Lori, and Brian to drift apart.
Eventually, Jeannette gets a call from her father asking for her to visit him; he is dying. Jeannette visits her father in their squatters' shack, and the two reminisce about her eventful childhood, and through it all, Jeannette realizes that, as much as her father was the cause of much stress and misery in her life, she still loved him very much.
A couple of weeks later, Rex Walls passes away. Jeannette re-examines her life choices leading up to the present day; ultimately, she ends her relationship with Eric and moves out of Park Avenue to settle down in a suburb in the West Side.
Five years later, Jeannette, now happily married and living on a country farmhouse, reunites with her family for Thanksgiving. Brian is married with a child, Lori brings Rose Mary with her, and news is that Maureen may be visiting from California very soon. During dinner, the family reminisces about Rex and decide to raise a toast to him; he was not a perfect father or husband, but life with him was never boring.