In April 2003, mountaineer Aron Ralston goes hiking at Utah’s Canyonlands National Park. He befriends hikers Kristi and Megan, and shows them an underground pool. After swimming, Aron parts ways with the hikers, and continues through a slot canyon in Bluejohn Canyon. While climbing, he slips and falls, knocking over a boulder which crushes his right hand and wrist against the wall. He calls for help but realizes that he is alone.
Ralston begins recording a video diary to maintain morale as he chips away parts of the boulder to try and free himself and tries to keep warm at night. He rations his food and water to survive the ordeal. He sets up a pulley using his climbing rope in a futile attempt to lift the boulder.
Over the next five days, Ralston tries using his multi-tool to cut himself free, but the blade is too dull to cut bone. With no water available, he is forced to drink his urine. In his videos, he becomes desperate and depressed. He hallucinates about escape, relationships, and past experiences including a former lover, family, and Kristi and Megan. During one hallucination, he realizes that his mistake was that he did not tell anyone where he was going, and decides that destiny has trapped him with the boulder.
On the sixth day, Ralston 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. He wraps the stump to prevent exsanguination, and takes a picture of the boulder. He then rappels down a 65-foot rockface using his other arm and drinks rainwater from a pond. He meets a family on a hike, who alert the authorities, and a Utah Highway Patrol helicopter brings him to a hospital.
Years later, Ralston starts a family, continues climbing, and always leaves a note saying where he has gone.