Into Thin Air is the nonfiction account of the tragic events of the spring of 1996 on Mt. Everest, which at that point was the deadliest climbing season in the history of the mountain. Jon Krakauer, a writer and amateur climber, is a client on the Adventure Consultants climbing expedition; he serves as the book's narrator. The story opens with Krakauer on the summit of Mt. Everest, too exhausted and delirious to care about his accomplishment. As he begins the painstaking descent back down the mountain, a storm forms and quickly worsens while many of his climbing teammates are still high on the summit. While he survives, the storm would eventually claim the lives of 8 climbers, with 4 more climbers dying in unrelated events that same season.
The story then starts from the beginning with an account of the history of human exploration of Mt. Everest, stretching back to 1852 when it was first confirmed as the world's highest mountain. For 101 years after that, climbers tried and failed to reach the summit, with many losing their lives in their attempts. It wasn't until 1953 that Sir Edmund Hillary and Tenzing Norgay became the first men to summit the mountain, thereby becoming celebrities around the world. Their accomplishment sparked a new wave of interest in Mt. Everest, and by the 1980s, guided expeditions to the summit became popular among amateur climbers who could afford the steep price tag. This led to widespread criticism about the over-commercialization of the mountain. Krakauer is offered an assignment to join one of these guided expedition and write about the phenomenon in Outside magazine, and although he worries about his ability to reach the summit, he can't resist the opportunity. As an amateur climber, summiting Mt. Everest has been a dream of his since childhood.
Krakauer leaves his home in Seattle in late March 1996 and meets his teammates in Kathmandu, Nepal. Rob Hall, the leader of his expedition is a celebrated climber from New Zealand with an exceptional record of guiding clients to the summit of Mt. Everest. His Adventure Consultants company has such a strong reputation that he charges $65,000 a head for a spot on his expeditions, more than any other company. There are seven other clients on Krakauer's team: Beck Weathers, John Taske, Yasuko Namba, Lou Kasischke, Frank Fishbeck, Stuart Hutchinson, and Doug Hansen. They are all amateur climbers with limited experience, and Krakauer worries about attempting such a challenging climb with strangers he doesn't know or trust. But this is the nature of guided expeditions, and he is reassured by Hall's leadership, along with Andy Harris, the team's senior guide.
The trek begins in the village of Lukla, and the first stretch to Everest Base Camp is easy and pleasant. As the team hikes through local villages, Krakauer meets the Sherpa, an ethnic group indigenous to the Himalayan region of Nepal. As skilled climbers accustomed to life at high altitudes, the Sherpa are often hired as expedition guides, porters, and general staff, linking the region's economy to the seasonal influx of foreign climbers. The group is blessed by a Buddhist monk and passes by a renowned altitude sickness clinic in Pheriche before arriving in Lobuje, a dirty, crowded village. They are delayed there as Hall assists with a rescue operation higher on the mountain, causing Krakauer and other team members to develop illnesses as a result.
On April 8, the team reaches Everest Base Camp, a collection of tents and temporary structures at 17,600 feet that serves as the staging ground for summit bids. There, Krakauer meets Scott Fischer, a friend and rival of Hall's who is leading an expedition under his young company, Mountain Madness. Krakauer reveals that Hall and Fischer competed to have him assigned to their respective expeditions, eager for the publicity that his Outside magazine article would generate. The team begins feeling the effects of altitude sickness--exhaustion, loss of appetite, and nausea--as Hall prepares a detailed plan to help their bodies acclimatize. Over the next month, they would prepare for the summit bid by doing short runs to progressively higher altitudes. Hall's Sherpa staff had set up 4 fully stocked camps ahead of time that would serve as intermediate stops, roughly every 2,000 feet between Base Camp and the summit.
Krakauer struggles during their first run to Camp 1 through the Khumbu Icefall, a dangerous maze of unstable ice blocks and deep crevasses, but he still performs better than many of his teammates. He is concerned upon learning that many of them hadn't had a chance to properly train or break in new equipment before departing on the expedition. But this is not unique to Krakauer's team: among the other expeditions on the mountain that season, an accident-prone Taiwanese team led by Makalu Gau and a dysfunctional South African team led by Ian Woodall are the biggest worries. Their presence on the mountain continues Mt. Everest's long history of attracting dreamers who are at best under-qualified to climb it.
Back at Base Camp, Krakauer speaks with his wife, Linda, over the camp's satellite phone. He reveals that she never supported his decision to climb Everest and that his risky but unshakeable climbing hobby had put a serious strain on their marriage. On the team's second acclimation run, Krakauer introduces Ang Dorje, the expedition's lead climbing Sherpa who assists Hall and Harris with their guiding responsibilities. Although the team successfully reaches Camp 2 at 21,300 feet, a Sherpa on Fischer's team comes down with High Altitude Pulmonary Edema (HAPE), a dangerous condition caused by lack of oxygen. This event, along with two frozen corpses that Krakauer spots along the trail, leaves him increasingly anxious and unnerved about the task ahead.
The team's final acclimatization run to Camp 3 is aborted due to dangerously cold temperatures, leading Lopsang Jangbu, the lead climbing Sherpa on Fischer's expedition, to worry that the climbers that season have done something to anger the spirit of Mt. Everest. Nevertheless, they make another attempt the next day, this time successful. Krakauer worries that his presence on the expedition, and the threat of what his future article might expose, is adding unhealthy pressure on his guides and teammates to try and prove themselves. He begins to respect them more as he sees that each teammate, like himself, has a powerful drive and sense of purpose that has kept them going despite their inexperience and battered physical condition. Having completed the final run, Hall sets May 10 as their summit day, aiming to take advantage of a forecasted small window of good weather at the top.
The team's summit bid begins from Base Camp on May 6, with Hall emphasizing the importance of putting judgement ahead of ambition, and setting a strict turnaround time of 2:00pm on summit day (May 10) regardless of their progress. Early in the ascent Fischer looks uncharacteristically tired. Krakauer largely blames this on Anatoli Borukeev, Fischer's skilled but impatient senior guide who has been neglecting many of his responsibilities and leaving Fischer to pick up the slack. The guides hand supplemental oxygen canisters and masks to the clients at Camp 3 to help compensate for the dangerously low oxygen levels above 25,000 feet. This altitude marks the beginning of the "death zone," where the negative effects of thin air on the human body increase dramatically.
At Camp 4, a fierce windstorm threatens to derail the summit bid; however, the wind subsides just in time, creating perfect summiting conditions. Krakauer's entire team of 8 clients departs camp for the summit, shortly followed by Fischer's team and Gau's team. In total, 33 climbers attempt the summit on May 10, leading to frustrating bottlenecks and slowing down the pace. Lopsang exhausts himself assisting Fischer's client Sandy Pittman and is unable to take his important position at the front of the line, while Hutchinson, Taske, and Kasischke reluctantly abandon the bid. Krakauer reaches the summit at 29,028 feet shortly after 1:00pm, ahead of most of the other climbers. He stops only briefly and feels no sense of awe or triumph, consumed instead by dread at the thought of descending back down the mountain. On the way down, it begins to snow and visibility quickly worsens. Krakauer's progress is extremely slow and painful, made worse by oxygen deprivation limiting his mental capacity. He runs into Weathers, standing still in the blizzard and nearly blind due to a severe eye condition. However, he leaves Weathers alone, confident that Hall's junior guide Mike Groom is shortly behind and can better assist him. Krakauer eventually reaches Camp 4 after 6:00pm with the blizzard still raging. He falls asleep in his tent thinking that the others made it back as well.
The story returns to the summit to recount what actually happened to the rest of the group. At 2:10pm, already after the designated turnaround time, all climbers except Fischer and Hansen have reached the summit. Neil Beidleman, Fischer's junior guide, decides he can't wait for Fischer any longer and starts descending with 5 Mountain Madness clients. They eventually catch up to Groom, who is struggling to support both Namba and Weathers. Their combined group reaches the general area of Camp 4 around 6:45pm, but the blizzard is so intense by then that they can't locate the tents. Desperate and disoriented, they wander aimlessly before Beidleman decides they have no option but to huddle together and wait out the storm. Eventually the storm calms down enough for Beidleman and Groom to find the camp and send Boukreev to rescue the clients who were too weak to move. Weathers and Namba appear to be already dead when Bourkeev finds them, but by 4:30am he leads the rest to safety.
The next morning, Krakauer is shocked to learn of the others' fates. The group at Camp 4 learns that Fischer is still missing and Hall is alive, stranded on the summit. The day before, Fischer didn't reach the summit until 3:40pm; at that time, he found Lopsang waiting for him and Hall waiting for Hansen. This group, along with Gau, quickly turns to descend, but Hansen runs out of oxygen and is unable to move shortly afterwards. Hall radios Harris requesting emergency oxygen, and despite it being already 5:00pm, Harris turns and hikes back up the mountain to assist. Fischer and Gau, both extremely weak and without oxygen, stop descending around 8:00pm and tell their Sherpas to go ahead and summon a rescue party. No one hears from Hall until 5:00am the next day, when he radios Base Camp informing them that Harris and Hansen are dead. Every expedition in the area is now aware of the situation and takes turns trying to convince a weak and confused Hall to descend as fast as possible, to no avail. Base Camp patches Hall's pregnant wife through from New Zealand, who is the last person to speak with him.
A Sherpa mission to rescue Fischer and Gau ends up only saving Gau after determining that Fischer is beyond saving. A second mission to locate the bodies of Namba and Weathers finds them both still alive, albeit barely. They are also left behind after determining that they are beyond saving, and Beidleman gathers the remaining Mountain Madness clients to begin descending. Another expedition arrives at Camp 4 ready to assist as Weathers miraculously stumbles into camp half-blind and severely frostbitten, having regained consciousness after being left for dead. The next morning, May 12, Krakauer and his reaming teammates begin the long and dangerous descent. They reach Camp 2 in the afternoon, where a Nepali army helicopter is able to evacuate Weathers and Gau, both in critical condition.
The rest of the group arrives at Base Camp the morning of May 13, and Krakauer immediately breaks down into tears. News of the tragedy has already spread around the world, and back in Kathmandu the survivors face swarms of reporters demanding to hear their story. When he finally returns to Seattle, Krakauer has a very difficult time working through his grief and guilt. While Kasischke and even Weathers, badly maimed by frostbite, are able to move on, many of the survivors struggle to find peace. The book closes with a discussion between Krakauer and Beidleman, who admits that he is still haunted by the memory of Namba and blames himself for her death.