The stories in "The Third Man Factor" are much alike: During a life-threatening event, each person experienced the close presence of a companion and helper.

The term was coined by adventurer Ernest Shackleton, who, with two members of his crew, made a perilous trip in 1915 to get help after his ship, the Endurance, was trapped by pack ice in the Weddell Sea adjacent to Antarctica. During the grueling trek, Shackleton said he and his companions felt that someone else was among them. "It seemed to me often that we were four, not three," he wrote.

Geiger also experienced the Third Man factor as a child when confronted by a rattlesnake. The presence he experienced kept him calm until his father could snatch him to safety.

"These occurrences 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," Geiger writes.

The experience may be an attempt by the brain to maintain stimulation in a monotonous environment, he writes. But, he says, there's more to it. It may also be an evolutionary development that helps to ensure survival.

Geiger spent six years studying and researching the syndrome and presents a number of factors that might cause it - ranging from scientific to mystical.

"The Third Man impresses those who experience the phenomenon with the vivid belief that they have come into contact with an unseen being of compassion and beauty, and, for some, a greater power," he writes.

The experience is a "real and potent force for survival," writes Geiger.

He also maintains the ability to access the power might be the most important factor in surviving against "seemingly insurmountable odds." Unfortunately, he doesn't say how to access it.

The book offers a fascinating look at the phenomena through the eyes of those who have experienced it and invites speculation about our beliefs.