It’s the stuff of nightmares–and now a powerful film as well. The British-made documentary “Touching the Void” re-creates the ordeal of two young British climbers, Joe Simpson and Simon Yates, who were trapped on the flank of Siula Grande, a forbidding Peruvian peak, back in 1985. So how was the moral crisis resolved? The thousands who read Simpson’s best-selling memoir, also called “Touching the Void,” will already know: Yates cut the rope.

But the full force of both book and movie lies in the sequel to that decision. Against all odds, Simpson survived a 50-meter plunge into a crevasse. Unable to climb out, he crawled down into the abyss in search of a route back to the daylight. His luck held. Driven by cussed determination, he hopped and crawled down the mountainside for two agonizing days, reaching base camp in a state of delirium just as Yates was preparing to leave.

For filmmakers, it’s a story with some blockbuster ingredients: a critical dilemma, a friendship tested and one man’s contest with the implacable forces of nature. Small wonder that Hollywood was interested. A score of producers sought the rights to Simpson’s memoir. Tom Cruise was once lined up for the lead role. But the project languished; along with its epic qualities, the tale posed awkward problems–particularly, how to dramatize the interior monologue at the core of the book?

The solution comes from British documentary maker Kevin Macdonald, who collected an Oscar in 2000 for “One Day in September,” a retelling of the terrorist attacks at the Munich Olympics. His approach is deadpan. Actors and stuntmen play out the story on the mountainside. But most of the narrative comes from Simpson and Yates themselves, speaking directly to the camera against a neutral background. Simpson, in particular, tells an articulate tale–but don’t expect tortured self-analysis or lyrical description. Mountaineers, especially British ones, are shy of gut-spilling.

So much the better. The dispassionate style throws into relief the horror of the events described and the awesome savagery of the Andes backdrop. For good measure, it also highlights the speakers’ occasional musings on the metaphysical. Simpson, a long-lapsed Roman Catholic, notes his own unshakable atheism. Even when facing death he recollects feeling no urge to pray. Beyond, he concludes, lies nothing but the infinite void. Yet the calm delivery is deceiving; neither man has quite escaped psychological scarring. Simpson has told how he suffered posttraumatic stress after revisiting the Andes with the film crew. And since filming ended, Yates has broken off all contact with the director. He’s reportedly unhappy with the film.

What has survived is the relationship between the two protagonists. As the movie makes clear, Simpson never questions Yates’s decision to sever the rope. Indeed, among his first actions on regaining base camp is to thank Yates for his help after the original accident. One reason he chose to publish his memoir was to exonerate Yates, who came under attack for breaching a taboo of the mountaineering fraternity. As a climber, Simpson understood the need for pragmatism in moments of crisis. He summarizes his own attitude with heroic understatement. Climbing was “fun,” he says. “But sometimes things went wrong; then it wasn’t fun.” For proof, just watch “Touching the Void.”