Joe Simpson and Simon Yates set out to climb the unclimbed west face of Siula Grande in the Peruvian Andes in 1985, and get down again only by accident. On the descent Simpson shatters his leg, and Yates, lowering him on a rope in a whiteout, ends up holding his partner's full weight over a cliff with no way to see what's below. He cuts the rope. Simpson falls into a crevasse and, against every likely outcome, climbs out and crawls for three days back to camp on a broken leg with no food or water. The film cuts between Simpson and Yates recounting the climb straight to camera and reenactments shot on real mountain terrain, so the physical details, ice screws, ropes, the sound of falling, carry as much weight as the interviews. Yates's decision to cut the rope became notorious in climbing circles, and the film lets both men explain it without softening how close it came to killing Simpson anyway.