Christopher Johnson McCandless travels to Alaska's Denali National Park and Preserve in April 1992 and arrives in the isolated region of Healy. He finds it so hard to get a ride and picks up a new book on local flora and fauna. The man who drops Chris off gives him gumboots and his number because he sees how unprepared Chris is and asks him to ping him back if he ends up alive. From there, he walks into the wild all alone. 

He finds a place for shelter. A city bus that Chris refers to as "The Magic Bus" is abandoned and used as a makeshift camp. He enjoys the solitude, the splendor of nature, and the adventure of living off the land. As he prepares for his new existence in the wild, he hunts with a 22-caliber rifle, reads literature, and writes a notebook.

Flashback

Chris earned a high honors diploma from Emory University in May 1990. His parents throw him a graduation celebration at a hotel. Chris has a college fund of $24,500 and 68 cents. They say they'll give him a new car as a graduation present to replace his junker. He becomes enraged and admits that his junker is still functional and that he does not require a replacement.

To experience living in the woods, Chris burns his credit cards and identity, gives his savings to Oxfam America, and embarks on a cross-country drive in his Datsun 210. Chris's car is submerged in a flash flood at Lake Mead. He takes away the number plate of his car and burns the remnant amount he had. He abandons it and starts traveling. He wakes up in Lake Mead, Arizona, in July 1990, takes the alias "Alexander Supertramp," and dumps his car’s number plate in a dumpster. Chris's final grade reports, which were mostly 'A's, had been mailed to his parents by Emory University.

His parents start to worry more and more about this. He didn't have a phone, so his parents drove to Atlanta to surprise him. However, they needed to be made aware that he had left the rental house two months prior. All of their letters to Chris have been returned to them by the post office in a bundle. He leaves without telling his parents or his sister, Carine, what he's doing or where he's going, and he doesn't get in touch with them again.

He travels to the Pacific Crest Trail in northern California in August 1990. There he meets the bohemian couple, Jan and Rainey. He notices the distance between them. Chris and Carine were forced to watch the violence that occurred between his father, Walt McCandless, and his mother, Billie McCandless when they were young. Their parents drew them together to choose one of them to live with as part of their divorce plan. Fortunately, the divorce did not occur, but the conflicts continued. Finally, Chris and Carine turned themselves off by refusing to stop their parents. 

Rainey informs him that his relationship with Jan is deteriorating, and Chris assists in rekindling it. Then Chris abandons them before they wake up in the morning. In early September, his parents receive a call from Annandale police informing them about Chris's abandoned car, which leads them to the conclusion that Chris was acting to avoid being found. 

Chris moves to Carthage, South Dakota, on September 10, 1990, to work for Wayne Westerberg's contract harvesting business. As Wayne advised, Chris on the other side talks with Kevin about how to survive and live in the wilderness, as well as the vital items that must be retained. After Westerberg is taken into custody for satellite piracy, he departs. To find him, they engaged a private investigator. 

Chris spent the summer after graduation driving across the country, where he visited some of their family buddies in California and learned something about his father, Walt. Walt was already legally married to someone else.

He had another son with his first wife, Marcia, even after Chris was born. He became unhappy with modern society after realizing that he and his sister, Carine, were born outside of marriage. As a result, this fact redefined Chris and Carine as retarded children.

And Billie, to the young mistress's shame and embarrassment, became his accomplice in deception. Chris saw their phony marriage and Walt's denial of another son as murders of everyday truth. Those insights sank to the core of Chris' identity. They fabricated his entire childhood. Chris never informed them of his knowledge.

Despite park authorities' warnings that Chris cannot kayak down the Colorado River without a license, he ignores them. On the way, he comes across Sonja and Mads relaxing by the river. When Mads asks Chris where he's going, he claims he has no idea. So Mads recommends that Chris kayak along the specified route to reach Mexico. Chris continues in this manner. He decides to call the family instead, and out of compassion, Chris turns over his penny to the needy old man who was on the phone with his loved one. Chris was being driven by something other than revolt or rage. He has been apprehended by the authorities and is being investigated for illegally crossing borders. 

Chris explains that he spent 36 days in a cave and entered Mexico via a spillway at Morelos Dam. He claims to have ferried his kayak across the desert and got a ride to Golfo, and he admits that he returned to the United States on foot after losing his kayak in a dust storm. He then boards the train carrying goods bound for Los Angeles after failing to find a ride. But shortly after arriving, he feels "corrupted" by contemporary society and departs. After being apprehended and assaulted by railway police for violating the law, he is forced to resume hitchhiking. Chris has been missing for almost a year. His parents' rage, desperation, and guilt began to give way to suffering. The anguish seemed to draw them closer together. When Billie sees a stray, she convinces herself that it's Chris, her son.

When Chris lands at Slab City, in the Imperial Valley, on December 18, 1991, he runs into Jan and Rainey once more. He also meets Tracy Tatro, a young woman. Jan discusses her past, revealing that she became pregnant when she was very young, believing that the baby would bring them peace, but her spouse abandoned her. Then she met Rainey, which was wonderful for a while. Reno was a teenager at the time, and he was on his way to becoming his own man. And she hasn't heard from him in two years, she claims. She has no idea where he is right now.

Tracy expresses interest in him, but he declines to date her since she is underage. After the holidays, Chris keeps traveling in the direction of Alaska.

One month later, Chris is in Salton City, California. Ron Franz, an ex-army man, encounters Chris while they are camping close to Salton City. He is a retired widower who lost his family in a vehicle accident when he was serving in the US Army. He works with leather and lives alone in a workshop. Chris creates a belt outlining his trips, also thanks to Franz's leatherworking instruction.

Chris chooses to leave Franz after spending two months with him. Franz provides him with his old camping and traveling supplies and offers to adopt Chris as his grandson. Chris advises him to bring it up once he gets back from Alaska.

Flashforward

Chris manages to survive with the groceries that he discovers on the magic bus. Certainly, Chris' life becomes more difficult at the abandoned bus four months later, and he makes several bad choices. He uses a rifle to kill a giant moose in an attempt to live off the land, but he is unable to preserve the meat, so it spoils quickly. He becomes aware of the harshness of nature as his provisions run out.

Chris realizes that genuine enjoyment can only be had when it is shared with people, and he sets out from the wild to rejoin his friends and family. However, he discovers that the thaw has made the creek he crossed over the winter wide, deep, and turbulent, and he is unable to cross. He retreats to the bus after losing.

Chris gathers and consumes plants and roots out of desperation. He consumes a toxic plant after mistaking it for a similar one and getting sick. As he slowly deteriorates, he keeps a journal of his self-realization journey and ponders what life could have been like if he had been able to get back to his family. He says goodbye to everyone and then climbs into his sleeping bag to pass away.

Through his sister's narration, we came to know that moose hunters who passed by discovered his body two weeks later. Carine soon leaves Alaska and heads back to the Eastern Seaboard with her brother's ashes in her backpack.