Susanna Kaysen, an eighteen-year-old in April of 1967, agrees to enter McLean Hospital, a residential psychiatric facility in Massachusetts. Although she plans to stay only a few weeks, Kaysen remains at McLean for nearly two years. The doctor who forcefully advocates her committal to a mental hospital interviewed Kaysen for only twenty minutes.

Kaysen tells the story of the people and experiences she encounters at McLean in a series of nonchronological vignettes. Among the patients admitted to her ward, Kaysen describes Polly, a kind patient with disfiguring, self-inflicted burns to her face and body. Lisa, another patient, entertains Kaysen with her escape attempts and exaggerated contempt for hospital authorities. Kaysen’s roommate, Georgina, struggles to maintain a relationship with Wade, a violent and unstable boyfriend from another ward, who tells the girls seemingly outlandish stories about his father’s exploits with the CIA. The twin obsessions of roasted chicken and laxatives make a newly arrived patient named Daisy the object of much speculation. Daisy ultimately leaves the hospital, only to commit suicide on her birthday.

One day, James Watson, a Nobel laureate and friend of the Kaysen family, visits Kaysen. He offers to take her away from the cold, prisonlike facility, but she rejects the offer, convinced that she should stay the course of her treatment. Kaysen discloses an unsuccessful suicide attempt involving an aspirin overdose in high school. She considers the nature of her illness, which includes difficulty making visual sense of patterns, and wonders whether sanity is merely an illusion that people construct to feel “normal.” Because many famous people have been residents of McLean Hospital, Kaysen speculates that creative minds, especially poets’, may be prone to mental illness.

The hospital’s strict rules dictate patients’ daily routines. Nurses perform “checks,” periodic visual appraisals of a patient’s activities and whereabouts, according to a schedule that corresponds to the severity of the patient’s illness. The staff confiscates any possessions that might inflict injury, even earrings and belts. Field trips outside the hospital walls are rare and require a complex system of patient-to-nurse accompaniment.

Lisa Cody, a new patient, arrives and threatens the social position of a current resident, also named Lisa, who torments the new girl until she leaves McLean and falls into more desperate circumstances. At this point, Kaysen considers the twenty-minute consultation that resulted in her hospitalization. Analysis of hospital records is inconclusive, and Kaysen’s doubts about the accuracy of her memory leads her into a discussion of the nature of mental illness, which Kaysen believes falls into two categories: slow or “viscous” and fast or having “velocity.” Kaysen believes that both kinds of illness result in the same type of mental paralysis.

Kaysen introduces us to Valerie, the young head nurse, who wins the girls’ respect with her no-nonsense approach to the job and a willingness to stand up to the doctors. Dr. Wick, an older psychiatrist, has trouble relating to the youth culture of her patients and becomes uncomfortable during any discussion of sex. The girls uniformly detest Mrs. McWeeney, the evening nurse, who is decidedly old-fashioned in her dress, speech, and insistence on strict authority.

The year 1968 is an exciting and frightening year, and Kaysen and the other girls watch its tumultuous events unfold on television. Simply viewing the world’s turbulence temporarily calms them. The girls come to realize that they are sitting on the sidelines of the era’s events and their own lives.

Torrey, a methamphetamine addict from Mexico, arrives on the ward. Torrey’s parents are embarrassed by their daughter’s problems. When Torrey’s parents come to retrieve her, Lisa attempts to help her escape her parents, but Valerie doses Torrey with Thorazine to foil the plan. The other girls fall into a depression. Kaysen suffers an episode of depersonalization that leads her to attempt to tear open her hand to confirm that she has bones beneath the skin.

Kaysen’s wisdom tooth becomes infected, and Valerie takes her from McLean to a dentist in Boston. Kaysen becomes frantic when, upon waking from the general anesthesia, no one will tell her how long she was unconscious. She worries that she has “lost” time.

A new patient named Alice Calais enters the ward, but a mental breakdown leads to her transfer to maximum security. The girls visit Alice, whose condition and living arrangements sicken them. They vow never to let the same thing happen to them. Kaysen starts sessions with Melvin, a therapist with whom she begins an advanced form of analysis. Enthralled with the tunnels below the hospital, Kaysen struggles to convey their meaning to Melvin. She discovers she is Melvin’s first patient, and then she gladly leaves analysis behind.

As Kaysen heals, she searches for a job outside the hospital, quickly becoming acquainted with the widespread prejudice that haunts former mental patients. Even applying for telephone service or a driver’s license requires a doctor’s note. Kaysen resumes a relationship she began with a man she knew before entering the hospital and impulsively accepts his marriage proposal. Reflecting on the difference between the mind and the brain, Kaysen wonders whether doctors treat one at the expense of the other. She reveals her diagnosis: borderline personality disorder. Dissecting the medical definition of the disorder, Kaysen notes that it is much more commonly diagnosed in women than in men. She wonders to what degree sexism and psychiatric fads influence the diagnoses.

Some years after leaving McLean, Kaysen visits Georgina, now married and as eccentric as ever. Kaysen also runs into Lisa, who has a young child and lives in a respectable suburb. Kaysen detects traces of Lisa’s old personality beneath the persona of a suburban mother. In the final chapter, Kaysen reveals the origin of the title of the book, Girl, Interrupted. Separated by some twenty years, Kaysen stands in front of the painting at New York’s Frick Museum. The painting holds very different meanings on each occasion; the changing interpretation reflects Kaysen’s life experience.