Twenty-one years ago this month, on September 6, 1992, the decomposed body of Christopher McCandless was discovered by moose hunters just outside the northern boundary of Denali National Park. He had died inside a rusting bus that served as a makeshift shelter for trappers, dog mushers, and other backcountry visitors. Taped to the door was a note scrawled on a page torn from a novel by Nikolai Gogol:

Attention possible visitors.s.o.s.i need your help. I am injured, near death, and too weak to hike out of here. I am all alone, this is no joke. In the name of god, please remain to save me. I am out collecting berries close by and shall return this evening. Thank you, chris mccandless august ?

From a cryptic diary found among his possessions, it appeared that McCandless had been dead for nineteen days. A driver’s license issued eight months before he perished indicated that he was twenty-four years old and weighed a hundred and forty pounds. After his body was flown out of the wilderness, an autopsy determined that it weighed sixty-seven pounds and lacked discernible subcutaneous fat. The probable cause of death, according to the coroner’s report, was starvation.

It seemed more plausible that McCandless had indeed eaten the roots and seeds of the purportedly nontoxic wild potato rather than the wild sweet pea. So I sent some Hedysarum alpinum seeds I’d collected near the bus to Dr. Thomas Clausen, a professor in the biochemistry department at the University of Alaska Fairbanks, for analysis.

Shortly before my book was published, Clausen and one of his graduate students, Edward Treadwell, conducted a preliminary test that indicated the seeds contained an unidentified alkaloid. Making a rash intuitive leap, in the first edition of “Into the Wild,” published in January, 1996, I wrote that this alkaloid was perhaps swainsonine, a toxic agent known to inhibit glycoprotein metabolism in animals, leading to starvation. When Clausen and Treadwell completed their analysis of wild-potato seeds, though, they found no trace of swainsonine or any other alkaloids. “I tore that plant apart,” Dr. Clausen explained to Men’s Journal in 2007, after also testing the seeds for non-alkaloid compounds. “There were no toxins. No alkaloids. I’d eat it myself.”

Hamilton is neither a botanist nor a chemist; he’s a writer who until recently worked as a bookbinder at the Indiana University of Pennsylvania library. As Hamilton explains it, he became acquainted with the McCandless story in 2002, when he happened upon a copy of “Into the Wild,” flipped through its pages, and suddenly thought to himself, I know why this guy died. His hunch derived from his knowledge of Vapniarca, a little-known Second World War concentration camp in what was then German-occupied Ukraine.