In 1953, Austrian mountaineer Herman Buhl became the first person to climb Nanga Parbat in the ­Himalayas—at 26,660 feet, the ninth tallest peak in the world. He climbed by himself and not far from the summit was forced to spend the night out in the open without a sleeping bag or tent. It was an agonizing ­bivouac, but Buhl survived—in part, he later wrote, ­because he sensed that he shared the ordeal with a ­companion. "I had an extraordinary feeling," he wrote, "that I was not alone."

Accounts of experiencing a supportive presence in extreme situations—sometimes called the "third-man phenomenon"—are common in mountaineering ­literature. In 1933, Frank Smythe made it to within a 1,000 feet of the summit of Mount Everest before ­turning around. On the way down, he stopped to eat a mint cake, cutting it in half to share with . . . someone who wasn't there but who had seemed to be his ­partner all day. Again on Nanga Parbat, on a 1970 climb during which his brother died, Reinhold Messner ­recalled being accompanied by a companion who ­offered ­wordless comfort and encouragement.

In "The Third Man Factor," John Geiger, a fellow at the University of Toronto, presents many accounts of such experiences, and not only from climbers. Among those who have felt a ghostly companionship he cites Charles Lindbergh on his solo flight across the ­Atlantic in 1927 and the last man to walk out of the South Tower of the World Trade ­Center before it ­collapsed on 9/11. "Over the years," Mr. Geiger writes, "the ­experience has ­occurred again and again, not only to 9/11 survivors, mountaineers, and ­divers, but also to ­polar explorers, ­prisoners of war, solo sailors, shipwreck ­survivors, aviators, and ­astronauts. All have ­escaped ­traumatic events only to tell strikingly similar stories of having experienced the close presence of a companion and helper." Mr. ­Geiger's book is a highly readable, often gripping, ­collection of survival stories, alongside a survey of theories that attempt to explain the third-man phenomenon.

One of the most famous stories involves polar ­explorer Ernest Shackleton, who set off with two ­volunteers, in January 1915, to fetch help for the crew of his ship the Endurance, then locked in Antarctic ice. ­After navigating perilous seas and crossing glaciers and mountains on foot, Shackleton recalled feeling that someone else was among them. "It seemed to me often that we were four, not three," he wrote. ­Shackleton's ­actual companions told him that they, too, felt the ­presence of another person. T.S. Eliot used the incident for a passage in "The Waste Land." ("Who is the third who walks always beside you?" Eliot wrote. "When I count, there are only you and I together.")

Mr. Geiger himself describes experiencing a third man himself when he was 7 years old and came upon a threatening rattlesnake, only to be snatched out of ­danger by his father—while some other presence stood by reassuringly. "These occurrences," Mr. Geiger writes, "suggest a radical idea—that we are never, really, truly alone, that we can summon someone—some other—in certain situations, most commonly in extreme and ­unusual environments." Mr. Geiger notes that ascetics and hermits have reported similar encounters.

The theories for explaining the third-man ­experience vary widely. Ron DiFrancesco, the 9/11 survivor who walked out of the South Tower, is convinced that God was by his side, and indeed a spiritual interpretation is common. Scientists, by contrast, have discovered how to evoke the sensation of a shared ­presence by stimulating the brain with ­electricity. Mr. Messner, the mountaineer, leans toward the idea that the third-man phenomenon is a survival strategy hard-wired into the brain. "The body is ­inventing ways to provide company," he says.

Although Mr. Geiger never shoots down any specific theory, he seems to endorse a biochemical ­explanation. "It is possibly even an evolutionary ­adaption," he writes. "Imagine the advantage for ­primitive man, ­perhaps ­separated during a hunt, alone far from his tribal group, to have the guiding hand of a companion pointing the way home." But the ­phenomenon is not limited to ­people in extremis. Mr. Geiger notes that children often experience ­real-seeming "imaginary friends," while ­widows and widowers say that they feel the presence of a ­deceased spouse.

"The Third Man represents a real and potent force for survival," Mr. Geiger writes, "and the ability to ­access this power is a factor, perhaps the most ­important factor, in determining who will succeed against seemingly insurmountable odds, and who will not." Mr. Geiger, however, is at a loss to explain why some can access this power and others can't.

He recounts the example of Maurice Wilson, an ­Englishman who most historians consider slightly ­unhinged. In 1934, Wilson decided to climb his first mountain: Everest. He actually made it to almost 22,000 feet (more than two-thirds of the way to the top). "I feel there is somebody with me in tent all the time," he wrote in his diary. He pressed on alone in ­terrible ­conditions, leaving his Sherpa porters behind. Soon ­after, he died. "It is unknown," Mr. Geiger writes, "if his invisible companion stayed with him during his final hours." The lesson? "There is no saving the life of one who will not be saved. The Third Man requires a willing partner."

Of course there may be many others who, like ­Wilson, ­experienced a third man and died ­anyway—but who left no account. Or still others who have survived ­extremity without a ghostly ­helpmeet. ­Ultimately Mr. Geiger's search for answers is inconclusive. His ­optimism, however, never wanes.

"Imagine the impact on our lives if we could learn to access this feeling at will," he says. "There could be no loneliness with so constant a companion. There could be no stress in life that we would ever again have to ­confront alone." In the meantime, we have Facebook.

—Mr. Ybarra writes about extreme sports for the ­Journal's Leisure & Arts page.

John Geiger opens his book with a terrifying story of the last person to escape the South Tower on 9/11, one of only four from above the 81st floor; he follows it with another horrific story of a mountain climber swept 2,000 feet by an avalanche, who regained consciousness with a broken back, a fractured arm, cracked ribs, torn knee ligaments, internal bleeding, broken nose and teeth and open wounds; then another about a scuba diver lost in a cave. What they have in common is that at the edge of giving up, they felt the presence of a guide who told them not to give up. Not only that, the presence dispensed both encouraging and practical advice: Get up, run through the fire, calm down, follow the white rope, keep going. The same thing happened to Ernest Shackleton and his two companions as they crossed the mountains and glaciers of South Georgia; it happened to Joshua Slocum when he fell ill as he circumnavigated the globe. Charles Lindbergh encountered a presence in his fuselage as he struggled to stay awake on his trans-Atlantic flight. In the words of the author, "This presence offered a sense of protection, relief, guidance, and hope, and left the person convinced he or she was not alone but that there was some other being at his or her side, when by any normal calculation there was none." This phenomenon is called the Third Man Factor, and to some will sound like fantasy or religious belief or simple delusion. It also sounds like a rare happening, but as Geiger shows in this fascinating book, the experience is almost a commonplace occurrence among polar explorers, mountaineers, astronauts, shipwreck survivors--anyone who has been put in a near-death situation.

Some experience the sensed presence as an angel or some other supernatural agency; others see it a something from within, a psychological or physiological mechanism. Attempts to explain this emanation are fascinating. Common triggers are the stresses of boredom, of loss of a companion, of injury, of extreme external conditions. Geiger says there is also an internal psychological variable--he calls it the muse factor, an openness to experience or state of receptiveness. This experience is in no way characteristic of delirium; in fact, many climbers say that Third Man powers compensate for altitude-related mental impairment. Whether the explanation is neurological or divine or both, this period of transcendence over an immediate, dire situation is genuine. Vincent Lam, in his introduction, says, "Certain complex experiences . . . are part of the mystery of being human, the wispy territory in which we exist somewhere between our ambitious science and our daily frailties. [In this mysterious gap], we find that things occur that are not easily explainable, but are no less real for that."--Marilyn Dahl

Shelf Talker: A fascinating, thrilling account of people in extreme situations and the Third man, the presence that appears to guide and encourage them.

A scientific mystery or divine intervention is how Geiger, the editorial board editor at the Globe and Mail and author of Frozen in Time, describes “The Third Man Factor,” the human knack of facing deprivation and possible death with an unseen presence pointing the path to survival. He researched these visitations for six years, chronicling their history in harrowing life-and-death events with mountaineers, sailors, divers, aviators and polar explorers. It is to Geiger's credit that he stresses the very human need to endure and survive through critical times in the included anecdotes over the sometimes convoluted scientific jargon, especially the gripping tales of the last 9/11 survivor Ron DiFrancesco, NASA astronaut Jerry Linenger aboard the Mir space station and merchant seaman Kenneth Cooke, who paddled in shark-infested waters. Whether this “guardian angel” factor is neurological or divine, Geiger's fresh, insightful book will tell readers “things that are not easily explainable, but no less real for that.” (Sept.)

An award-winning Canadian author uncovers spiritual guardians who aid those in states of crisis.

Globe and Mail editorial board director Geiger (Nothing Is True, Everything Is Permitted: The Life of Brion Gysin, 2005, etc.) presents dozens of examples of people who have encountered an unseen presence, or, as T.S. Eliot wrote in The Wasteland, "the third who walks always beside you." Typically, the "Third Man" is either sensed or manifests in a shadowy formation appearing amid hopeless circumstances proffering words of encouragement and direction. Ron DiFrancesco, one of the last survivors to escape the South Tower on 9/11, chronicles an unseen "benevolent helper" who guided him down through a fiery, smoke-choked stairwell and disappeared soon after. Crushed by an avalanche, a mountain climber received inspiration from an "invisible being" who led him to safety. A panicked diver lost sight of her guideline within a maze of undersea caves and was inexplicably guided to the surface. Members of a doomed Antarctic expedition describe their encounter as having "spiritual significance." Geiger also writes of sailors cast adrift, biblical theologians, lonesome widowers and postpartum women, all of whom claim that their individual rescues were caused by angelic interaction. Even famed aviator Charles Lindbergh reported seeing friendly "phantoms," though a psychological evaluation attributed his claim to monotony and boredom. The phenomenon's counterpoint suggests stress, depression-induced hallucinations, malnutrition, social stagnancy and extreme environmental exposure as probable contributors to the appearance of the Third Man. Geiger evenhandedly presents both sides of this mysterious anomaly in clear, concise language. Ultimately, he labels the Third Man an "instrument of hope...the belief-the understanding-that we are not alone."

An intelligent rendering of a chilling phenomenon.