What do you do when one of your idols turns out to be a fake? How do you reconcile his influence on you, and on the world, with his dishonesty? These questions drive journalist Susannah Cahalan’s forthcoming book The Great Pretender (Grand Central, Nov.), which centers on David Rosenhan, a Stanford psychologist whose reform-spurring research into insane asylums may not have been as scrupulous as it should have been.

Cahalan, a former reporter for the New York Post, has a personal investment in studies of mental illness. Her first book, Brain on Fire (Simon & Schuster, 2013), chronicled her experience with a rare autoimmune disease that was first misdiagnosed as bipolar disorder. When she encountered Rosenhan’s classic study, “On Being Sane in Insane Places,” she found that it reflected her own experience of crossing the border between “sane” and “insane.”

For the study, which was published in the early 1970s, Rosenhan and seven other people got themselves admitted to insane asylums by faking symptoms of mental illness. Their reports on their experiences in the asylums—and their struggles to prove themselves “sane” enough to be let out—shed unflattering light on how caretakers treated the mentally ill and hastened the closure of psychiatric institutions.

For Cahalan, the study captured the particular trauma of being labeled “insane,” even if only temporarily. She says, “This feeling of depersonalization, this feeling of doctors wanting to distance themselves from you, feeling ‘other,’ ” all of which resonated with her. But when she began to look into the story behind the study, which was originally published in the journal Science, she found troubling inconsistencies.

Cahalan gained access to Rosenhan’s files, as well as medical records from the insane asylums he studied. She also interviewed study participants who’d never spoken publicly about the experiment. (Rosenhan himself died in 2012.) Eventually, Cahalan began to suspect that portions of the study had been fudged. “The questions kept coming,” she says.

Cahalan found it difficult to square the positive effects of the study with its scientific shakiness. Rosenhan exposed widespread maltreatment of mentally ill patients and inspired soul-searching in the psychiatric community. Should his mendacities necessarily negate that?

In Ken Kesey’s classic insane-asylum novel, One Flew over the Cuckoo’s Nest, he writes: “It’s the truth even if it didn’t happen.” It’s a line Cahalan returned to often while writing the new book.“There’s something about that, that I like,” she said. “Even though this study needs a kind of reckoning, I do believe it has a message.”

Today, 11-noon. Susannah Cahalan will sign The Great Pretender at Table 3.