The movie is technically a documentary, but it interviews only three men and the spoken narrative of the story belongs entirely to them. For the visual component of the story, three actors portray their real-life counterparts in the situations described by them.
In 1985, Joe Simpson and Simon Yates set out to climb Siula Grande, a 21,000-ft peak in the Andes, via a route never successfully completed. It seems like bad things are always happening in the Andes, doesn't it? These two climbers were no exception. I won't go into the details of what went so horribly wrong with their expedition so that you can get the full effect of the incident if you watch the film. However, I will tell you that they both survived. This isn't a spoiler because, as I mentioned before, the climbers themselves are the ones telling the story in the documentary. I think Eric D. Snider said it best when he described his feelings watching the film in this way:
"I spent much of the film shaking my head in disbelief as I saw what men are capable of doing in dire circumstances, the extent to which people can be broken down and still come back. There were at least three points when I thought, 'Well, that's it, there's no way he can survive this,' followed immediately by the thought, 'But he obviously DID survive, because he's NARRATING THE STORY!'"
You may notice that the film is rated R. This is a shame for two reasons. Firstly, because that rating alone will scare away many viewers from this amazing movie. Secondly, and perhaps more tragically, is because they could have so easily gotten a PG-13 or even PG (except for "mature themes," maybe, since it is about a struggle against seemingly certain death) by cutting or editing two scenes. Those two scenes each feature a sequence of sustained profanity uttered by the actors in the re-enactment. If you mute it during those two scenes, you'll be fine. (I just felt bad for the actors, who have virtually no dialogue at all in the entire movie except for those scenes, and it's all profanity.)
Profanity aside, I think it's good for the soul to watch a life-affirming movie such as this one every once in a while. Some movies are life-affirming because of their message, or moral, or inspiring characters. This one celebrates life by showing us in great detail the lengths to which ordinary individuals will go to preserve it.