Unable to cross the Teklanika River, Christopher McCandless heads back to the bus. He hunts. He also underlines several key passages in Boris Pasternak’s Doctor Zhivago that address the prospect of living a modest life of service to others. He leaves an enthusiastic note beside a passage saying that happiness is only real when shared with other people. Krakauer interprets this to mean that he may have had an epiphany because of his journey. McCandless’s diary also suggests that he was planning to go back to society. In his diary, McCandless left a note that he had been sickened by wild potato or Hedysarumalpinum seeds. But this leads Krakauer to more questions. H. alpinum seeds contain a toxin when they begin to sprout, but why would McCandless have eaten so many sprouted seeds? McCandless could have confused wild potato with wild sweet pea, a similar-looking species.
Krakauer then relates his own attempt to verify that wild sweet pea could have poisoned McCandless. Did McCandless pick H. mackenzii instead of H. alpinum? Krakauer details the arctic explorations of Sir John Richardson, a Scottish adventurer who included in his journals an anecdote about a native woman who nearly dies from eating wild sweet pea. He recalls that, in his first article in Outdoor Magazine, he reported with confidence that wild sweet pea killed Christopher McCandless. But after its publication, he began to doubt that Christopher McCandless had eaten wild sweet pea. He investigates further, but scientists find no toxins in the samples of wild sweet pea Krakauer sends. Instead of reaching any conclusions, Krakauer continues to read scientific literature. After several years, he stumbles upon an article describing a mold that produces a toxic alkaloid.
Krakauer relates that he is convinced McCandless ate moldy wild potato seeds and was poisoned. He describes what it might have been like for McCandless to die of starvation and quotes from his last diary entries, which become terse. On his hundredth day in the wild, McCandless leaves a jubilant note that ends in the admission he will likely die. Krakauer then outlines yet another difficulty McCandless faced. Without a map, McCandless was unable to realize that he had only to walk a few hours north to find cabins, though he might not have found many supplies, since those cabins had been vandalized. Certain dogsledders and rangers in the area indeed suspected McCandless of the vandalism, but Krakauer expresses doubts that McCandless was responsible, since his diary never describes them.
In early August 1992, Christopher McCandless continues to try to hunt and cook food for himself. On August 12, 1992 he leaves a note and goes to forage for berries. Krakauer briefly speculates why McCandless didn’t then start an S.O.S. fire to attract a plane. No planes would have flown over the bus anyway and a fire would have harmed the wilderness McCandless loved. Krakauer then describes the symptoms associated with death by starvation and the last documents Christopher McCandless left behind. He tears out a page from a book called Education of a Wandering Man. The page contains some lines from a poem by Robinson Jeffers that describe death and stoicism. On it, McCandless writes a goodbye message claiming that he has had a happy life. In the last lines of Into the Wild, Krakauer describes the peace in McCandless’s eyes in the last photograph he took of himself and compares him to a monk.
The narrator returns with Billie McCandless and Walt McCandless to Alaska by helicopter. They go inside the abandoned bus where Christopher McCandless died. Billie McCandless enters first and reviews her son’s belongings. She smells a pair of jeans he left behind and tells her husband that they smell like her son. She also recognizes silverware he took from their house in Virginia. They leave behind a plaque memorializing McCandless’s death and leave a suitcase of supplies, including Christopher’s childhood bible, and a note urging runaways to contact their families. Both Billie McCandless and Walt McCandless admit they are glad they came. Billie specifies that she might have found Christopher’s decision to live in the wild admirable if he had not died. Krakauer and Walt and Billie McCandless get back into the helicopter. After takeoff, the bus dwindles in the distance and then vanishes from sight.
In Chapter Eighteen, Krakauer examines the mistakes and reversals that colored McCandless’s final days in detail, providing a final series of implicit answers to his investigation of McCandless’s fate and concluding Into the Wild’s primary plot line. The narrative works almost as a countdown, starting on July 8, 1992 with McCandless’s return to the bus after finding the Teklanika too flooded, pauses the narrative for a discussion of his physical decline, then enumerating each remaining day at a time. His quotations from McCandless’s diary adds to the poignancy and drama of these last days, as does the inclusion of the detail that McCandless wanted to leave the wild. His diary records that he is now trapped, despite his desire to return, lending the chapter a fatal tone at the same time that Krakauer builds narrative urgency.