In her acclaimed debut, "Brain on Fire: My Month of Madness," Susannah Cahalan documented the psychotic break she suffered at 24, a terrifying episode that ended happily when it was determined that she had a completely curable autoimmune disorder — a neurological problem rather than a psychiatric one. What she had been saved from became achingly clear when, on tour for the book, she was told about another young woman with the same condition. Misdiagnosed and mistreated for two years instead of just a month, this woman's cognitive abilities had grown so diminished that she could no longer care for herself.

Stunned by the precariousness of psychiatric diagnosis and the disastrous outcomes it can sometimes cause, Cahalan began the investigation documented in "The Great Pretender." This vital book, full of intelligence and brio, is a must-read for anyone who has mental illness issues somewhere in their life — i.e., everyone.

Cahalan's main focus is a study conducted in the 1970s by the late David Rosenhan of Stanford University. In it, eight patients, including Rosenhan himself, managed to get themselves diagnosed with schizophrenia and checked into mental wards simply by showing up and claiming that they were hearing voices. The "pseudo-patients" then spent from two weeks to 52 days institutionalized, treated and medicated (Rosenhan taught them to "cheek" their drugs) until they got themselves released, often with difficulty.

When the results of this study were published in Science magazine, humiliation rocked the psychiatric profession. The most significant long-range effects of Rosenhan's landmark work included the widespread closing of hospitals and the vigorous revision and expansion of the Diagnostic and Statistical Manual of Mental Disorders — the DSM-III. This book, "as important to psychiatrists as the Constitution is to the U.S. government or the Bible is to Christians," according to one of Cahalan's sources, was written with the specter of those eight false diagnoses hanging over every page.

Beginning with boxes of notes and an unpublished book manuscript, Cahalan sets out to find the research participants. It does not go well. Finally, after pursuing myriad clues and dead ends, after interviewing Rosenhan's family and colleagues, Cahalan begins to have serious doubts about the man's integrity. As the monument begins to crumble, Cahalan was "clinging to the hope that all this would work out like a Doomsday cult member clings to her belief that the end is nigh even as the sun rises the next morning."

By that point, you will be as caught up as she was. And though some questions remain unanswered, Cahalan crowns the work with a conclusion that offers chilling data about the credibility of research in all fields of science — yet finds a ray of hope for the benighted field of psychiatry.

Marion Winik is the author of "The Big Book of the Dead" and the host of the Weekly Reader podcast. She is on the board of the National Book Critics Circle.

The Great Pretender
By: Susannah Cahalan.
Publisher: Grand Central, 382 pages, $28.