Chapter Eighteen includes significant scientific research. Like other sections of Into the Wild, the chapter is rich in local detail, including descriptions of flora and fauna. However, the long passages tracking Krakauer’s investigation into the composition and relative likeliness of particular plants to have poisoned McCandless make the chapter highly forensic in tone. The narrator brings natural science, agriculture science and botany directly into the text, reading journals in these fields and interviewing scientists in an attempt to find answers. The revelation that a toxin produced by a mold likely killed McCandless brings to an end one of the book’s many investigative plots. It also frees McCandless’s character from the allegations of incompetence or stupidity associated with his story in earlier chapters. The length of the chapter is significant. Krakauer relates it took him years to stumble upon the existence of the toxic mold. Because Krakauer treats McCandless’s death as a mystery worth years of effort to unravel, he also argues for the ultimate significance of his life.

Extremely realistic description of the physiological and psychological effects of starvation convey to the reader the intensity of suffering McCandless must have endured. The narrator’s tone becomes clinical, almost detached, precisely because the reader must be given a clear understanding of what McCandless underwent in order to determine the value of his journey. Krakauer’s realism pushes the reader into his experience and also maintains a critical perspective. McCandless’s overall perseverance is celebrated in the final photograph Krakauer describes, a self-portrait McCandless took before he became too weak to leave the bus. Both suspense and irony are released in the book’s concluding image, which revisits the idea that McCandless was extremely happy in the wild, even when he was already beginning to starve. The narrator then returns to a spiritual motif linking McCandless and other seekers of life outside civilizations to the tradition of pilgrimage, monasticism, and asceticism.

The epilogue of Into the Wild attempts to further the narrative closure provided by the book’s last chapter. Christopher McCandless’s parents, Walt and Billie, are the most affected by his death. Staging catharsis for each of them by traveling with them to the site of his death allows Krakauer to shift from investigating McCandless’s mind to reflecting on the traces he left behind in the living. The book’s characterization of McCandless’s parents receives a final complication and extension: Billie, who has been portrayed as loving but overcome by grief, now appears as vulnerable but strong. Walt McCandless’s terseness and frustration with his son are converted into grudging respect, even tenderness and the desire that his memory be known to other people. A deep love for Christopher McCandless steadies and grounds the narrative, resolving the physical suffering he underwent and the grief his parents felt. The epilogue’s final image of the dwindling away of the bus underlines this new balance for all of Into the Wild’s characters and closes the book on a note of abstract, calm farewell.