In 1985, Joe Simpson and Simon Yates set out to climb the 21,000 feet Siula Grande mountain in the Peruvian Andesthe only mountain in the Peruvian range that hadn't yet been conquered. They were young, fit, skilled climbers and were confident that they would succeed where others would fail. Their story has become part of mountaineering legend.

Simpson and Yates' method of climbing was Alpine Stylemoving quickly up a mountain with the barest of supplies and no series of base camps. This approach left absolutely no room for error. Any problem they might encounter along the way would have extremely grave consequences.

Following a successful three and a half day ascent, disaster struck. Simpson fell and broke several bones in his right leg. His lower leg pushed through his knee joint, crippling him. At that altitude and in those remote conditions, this was effectively a death sentence.

With no food or water, severe dehydration and the ugly spectre of hypothermia before them, the climbers knew they had to get off the mountainand fast. Yates was determined to find a way to get his friend home. They each had 150 feet of rope, which tied together so that Yates could lower Simpson down the mountain 300 feet at a time. The only complication was that Yates had to stop after each 150 feet and signal for Simpson to give him enough slack so that he could get the knot past his harness. Each drop down the mountain was agonizing for Simpson, but Yates had no choice but to ignore his partner's cries. Both of their lives were at stake.

Things were progressing unexpectedly well when Simpson failed to respond to Yates' signal. Unable to move any further and having no idea why Simpson was not pulling at the rope, Yates positioned himself against the mountain face and waited in the blinding storm. He held onto the rope with all of his strength, but was all too aware that eventually his muscles would fail him and both would plummet down the incline. What Yates couldn't know was that he had unknowingly lowered the injured Simpson over the edge of a crevasse. Simpson was hanging over the sheer vertical face of the mountain.

Joe remained suspended, unable to climb back up the rope with frostbitten fingers and unable to communicate with Simon above him. Simon hung onto the rope for an hour, with his strength ebbing away and Joe's weight on the rope slowly pulling him towards the edge of the cliff. Eventually Simon realized he was faced with an unthinkable dilemma: he could hang on to the rope until they were both pulled off the mountain.

Logic would say that it would be better for only one man to die rather than both. But the biggest taboo that any climber can commit is to cut the rope that binds you to your partner. For a climber, it is unthinkable.

Certain they would both soon be pulled to their deaths, Yates cut the rope Based on Joe Simpson's international bestseller, "Touching the Void" combines dramatic and documentary techniques and is directed by Kevin Macdonald, the Academy Awardwinning director of "One Day in September."