So she set out to find the eight volunteers, all of them unnamed in the paper and identified only by pseudonyms in Rosenhan’s notes. She soon learned that the pseudopatient named “David Lurie” was Rosenhan himself, who died in 2012, after a series of debilitating strokes. She eventually met with two other volunteers. Only one of them was included in the study; the second was excluded for having “falsified aspects of his personal history,” Rosenhan wrote.

As Cahalan would learn, though, this volunteer was excluded for a very different reason. “HE LIKES IT,” Rosenhan wrote in his notes, clearly incredulous. The volunteer had been admitted into psychiatric care during a difficult time in his life and found himself benefiting from what he described as a supportive environment. Rosenhan had a story to tell about miserable institutions that abused their power, and here was a data point that would have complicated such an unremittingly grim portrait.

But there was more. Rosenhan apparently falsified parts of the paper itself. Some of it looked like carelessness, or sloppy note-taking, but Cahalan also caught him “filling in gaps with outright fabrications.” She obtained the record of Rosenhan’s admission to Haverford State Hospital in 1969, and was taken aback by the difference between what the admitting physician recorded and Rosenhan’s version in his paper.

“The Great Pretender” reads like a detective story, with Cahalan revealing tantalizing clues at opportune moments so we can experience the thrills of discovery alongside her. Her voice is warm and often charming, though she has a weakness for whimsical asides — “take that, oncology!” — and at one point describes Rosenhan’s son as “the kind of teddy-bear man you can’t help but hug.” But such amiability was probably what got some reluctant sources to talk. One man sent her some crucial information while he was in the last stages of pancreatic cancer; another source agreed to an interview at her nursing home just before her 100th birthday. Without Cahalan’s intrepid reporting, the truth of Rosenhan and his paper might have been lost.

Cahalan calls Rosenhan’s willful distortions “infuriating,” faulting him for having “missed an opportunity to create something three-dimensional, something a bit messier, but more honest.” She’s right. But if Rosenhan had published something less sweeping and more subtle, chances are it would have been forgotten while louder voices stole the show. By 1973, the American public was already primed to believe the more extreme story he set out to tell. His paper garnered so much attention precisely because its clear-cut anti-establishment narrative aligned so neatly with the anti-establishment times.

In the end, Cahalan treads a delicate line between condemning Rosenhan and forgiving him; for all his exaggerations and outright falsehoods, she says, “I believe that he exposed something real.” “The Great Pretender” shows Rosenhan and his paper for what they are, but it also shows us something else. Pretensions to certainty can be seductive, eking out a temporary tactical advantage, but their victories are often brittle. Once the veneer of impermeability gets cracked, it “breeds an anti-science backlash born of distrust,” Cahalan writes.

Instead of arrogance, her book counsels humility. As one Oxford psychiatrist haltingly puts it: “I think we should be honest about — acknowledge how limited our understanding is.”