In Kevin MacDonald's riveting film, two Englishmen, Simon Yates and Joe Simpson, recount their disastrous attempt in 1985 to scale the 22,000-foot Siula Grande mountain in the Andes. They managed the difficult climb to the top, but their descent was imperiled almost immediately by a snowstorm and an accident that badly broke Simpson's leg. Circumstances became so dire and disorienting that Yates, in a survival gambit, cut the rope that bound the pair, sending Simpson plunging into a crevasse. The two men -- one wracked with guilt, the other with a shattered leg, and neither aware of the other's situation -- make separate climbs down the mountain. That they succeed is known: Both men narrate the film today, while actors recreate their youthful ordeal. Beyond the absolute physical horror of this story to which armchair extreme-sports fans will thrill, is the emotional vicariousness of the worst ethical dilemma (at what cost does one save oneself?) and of the depths of human fortitude: that Simpson makes it down the mountain defies any reasonable expectation of survival. The filmed recreations benefit from close camerawork -- from boots slipping through powder snow to the cruel beautiful gleam of blue-ice glacier walls. How much more terrifying it would have been if MacDonald had chosen to use just the clank of the ice axe echoing in the great empty silence rather than lumber the film with an emotional score, but that's a small quibble for a film that kept me perched on the not-at-all dangerous edge of my seat. Squirrel Hill