In April 2003, avid mountaineer Aron Ralston goes hiking at Utah's Canyonlands National Park without telling anyone. He befriends hikers Kristi and Megan and shows them an underground pool before they head home. After that, Aron continues on through a slot canyon in Bluejohn Canyon. While climbing, a boulder he was hanging off comes loose and causes both to fall, which traps his right arm against the wall. Aron attempts to move the boulder but it will not budge; he also soon realizes he is alone. He shortly begins recording a video diary using his camcorder to maintain morale, as he chips away parts of the boulder with a pocket knife. Over the next five days, Aron rations his food and remaining 300ml of water, struggles to keep warm at night and is forced to drink his urine when his water runs out. He also sets up a pulley using his climbing rope in a futile attempt to lift the boulder.
Throughout the days, Aron becomes desperate and depressed and begins hallucinating about escape, relationships, and past experiences including his family and his former girlfriend, Rana. During one hallucination, Aron realizes that his mistake was that he did not tell anyone where he was going or for how long. On the sixth day, Aron has a vision of his future son, spurring his will to survive. He fashions a tourniquet from CamelBak tube insulation and uses a carabiner to tighten it. Then, using his knowledge of torque, he breaks the bones in his arm and, using the multi-tool, slowly amputates it. Aron then wraps the stump to prevent exsanguination and takes a picture of the boulder before rappelling down a 65 ft (20 m) rockface. He then finds some rainwater collected while descending down, and drinks the stagnant water due to dehydration and continues. Back in the desert, he spots a family on a hike and calls for help. They give him water and alert the authorities; a Utah Highway Patrol helicopter brings him to a hospital.
A textual epilogue reveals that years later, Aron got married and had a son. He also continues climbing, and always leaves a note telling his family where he has gone.
