Repeat after me: “We know they survived because they are up on the screen telling the story.” You’ll need to hold onto that thought tightly to get you through this almost unbearably tense re-enactment of a terrible mountain-climbing accident and the extraordinary determination and courage that got the climbers home.

In 1985, Joe Simpson (age 25) and Simon Yates (age 21) decided they would be the first climbers ever to climb the west face of the 21,000-foot Siula Grande in the Peruvian Andes. They made it to the top, but on the way down Simpson fell and shattered his leg. Yates risked his own life to help Simpson descend, lowering him 150 feet at a time with a rope holding them together. But when Simpson fell again and Yates could not see or hear him, the rope that connected them was pulling Yates to certain death. Yates, believing Simpson had to be dead, cut the rope. He searched for Simpson but could not find him. He managed to make it down to the base camp, frozen, dehydrated, and utterly devastated. His story is one of the great feats in the history of mountaineering.

But Simpson’s story is one of the great feats in the history of human endeavor. A dozen different times over the next four days he faced certain death, but even when he thought it was hopeless, he simply refused to give up.

When Yates believed that Simpson had fallen off the mountain, he had instead fallen into a 150-foot crevass. By going down further into the crevass instead of trying to climb out of it, he managed to escape. But that still left him alone, badly injured, frostbitten, with no food or water, no hope of rescue and no way to get down. Facing a series of obstacles that would challenge a mythological hero, Simpson persevered. Even when he accepted that death was inevitable, he still kept going because “I didn’t want to die alone.” At times angry, terrified, and delirious, he kept trying anything and everything he could think of to get back home.

Director Kevin Macdonald lets Simpson, Yates, and Richard Hawking, who was waiting for them at base camp, tell the story in understated British style, as two actor/climbers re-enact the story on the actual site. Incredibly, Yates and Simpson returned to the Andes for the filming and put on their gear and performed some of the re-enactments themselves.

Their story is gripping and, in their perseverance and dedication, deeply moving. Simpson’s first comment when he sees Yates is as heart-wrenching as any of his struggles. Their candid but matter-of-fact delivery is far more effective than any actor could muster. Even now, they seem so young and open-hearted, Yates with bright button eyes and ears like the guy in “Wallace and Gromit.” It was in part their youthful audacity that made it possible for them to survive. If they had been more experienced, they would have known that what they were trying to do was impossible.

Macdonald reaches his own summit with an electrifyingly thrilling movie that makes the mountain more than a setting, almost another character in the story. The sheerness of the slope, the friable “meringues” and “cornices” of snow, the sweep and sparkle of the ice — the mountain’s terrible beauty is alternately austere, majestic, implacable, ominous, and menacing.

Parents should know that the movie is extremely tense, with characters in the direst peril imaginable. They use some very strong language, completely understandable in the circumstances.

Families who see this movie should talk about Simpson’s statement that the important thing was to act, even if the decision was the wrong one. What made Simpson refuse to give up? Families should discuss Simpson’s comment in an interview with the Washington Post, that he owed his survival to having gone to a British boarding school: “When you’re used to being rejected, like being sent away when you’re a youngster, you become very good at hugging yourself. And I think if I hadn’t been like that, I wouldn’t have survived.” This is reminiscent of Wellington’s famous comment that the battle of Waterloo was “won on the playing fields of Eton,” though not quite the same point.

Families should also talk about the way Simpson broke the insurmountable challenge into possibly surmountable segments in order to keep himself going. How can we apply that to our own challenges? Do you agree with Simpson that Yates did the right thing in cutting the rope? Was there something they could or should have done differently? Were you surprised that Simpson returned to climbing? Note, too, how they responded to each successive potential disaster with not just determination but with a very expert assessment of all of the options. And consider these options — at one time, Simpson’s book was considered as the basis for a feature film with an actor like Tom Cruise. How would that have made it different? What do you think about the combination of documentary and re-enactment?

Families who enjoy this movie will also enjoy Cliffhanger, Vertical Limit and K2. They will also enjoy Eric Newby’s classic mountain climbing story, A Short Walk in the Hindu Kush.