While climbing in Monument Valley, siblings Peter (O’Donnell) and Annie Garrett (Tunney) lose their father, Royce (Stuart Wilson): after two falling amateurs leave the family dangling, Royce forces Peter to cut him loose to save Peter and his sister.
Three years later, Peter has retired from climbing and became a full-time wildlife photographer, while Annie went on to become a renowned mountain climber. Their relationship is strained, as Annie still blames Peter for the death of their father.
Peter reunites with Annie at the K2 Base Camp, where Annie is planning a summit attempt on K2. The expedition is funded by wealthy industrialist Elliot Vaughn (Paxton). Their team consists of Annie, Vaughn, renowned climber Tom McLaren (Nicholas Lea), and Pakistani mountaineer Ali Nazir.
The day before the climb Vaughn throws a promotional party with all the people at base camp. The gala is interrupted by reclusive Montgomery Wick (Glenn), reportedly the world’s best climber and K2 foremost expert, who asks if it will be Vaughn or the experienced McLaren who will be making the decisions during the climb, as the team cannot have two leaders. Vaughn states that McLaren is the leader and later explains that Wick is against him because his wife, a Sherpa guide, was one of the people who did not survive his previous expedition. During that climb, they were hit by a storm and got lost in the mountain. Wick’s wife died of pulmonary edema on their way down because she forgot her supply of dexamethasone, the only medicine capable of preventing it. Wick has never believed that story and has spent years trying to find his wife’s body.
The climb turns out to be a disaster, as Vaughn forces McLaren to continue despite the radio warning from base camp director Skip Taylor (Robert Taylor) of a storm approaching. As the storm closes in, the winds begin to wreak havoc and cause an avalanche. Annie, Vaughn, and McLaren fall through a patch of ice and become trapped in a crevasse, while the other expedition members are killed. Radio contact is lost, but Peter remains by the radio and hears Annie using static to send a Morse code signal to inform base camp that they are alive.
Peter manages to assemble a rescue mission with some of the climbers at base camp, including base camp director Skip Taylor, brothers Cyril and Malcolm (Le Marquand and Mendelsohn), who are experienced climbers looking for adventure, Monique Aubertine (Izabella Scorupco), who needs the money from the reward offered by Vaughn’s company, and Kareem Nazir (Alexander Siddig), who is Ali’s cousin and wants to help even if he knows that his cousin is already dead. Skip and Peter also visit Wick, who agrees to join in the rescue attempt but requests that Skip remain behind, as Wick says that he needs someone he can trust at base camp directing the mission.
The teams form, pairing experienced mountaineers with less experienced ones: Malcolm and Kareem, Cyril and Monique, and Wick and Peter. After an eventful helicopter drop-off, each team takes a different entry point up the mountain to increase chances of success. They each carry an old canister of nitroglycerine donated by the Pakistani Army to clear out the entrance to the crevasse.
Monique and Cyril encounter trouble when Cyril loses his balance and clings to the side of a cliff. After Monique secures her harness to him, the peak cracks, and Monique also falls over the edge. Their leaky nitro canisters explode beneath them while they hang from ropes. Cyril is able to climb back up, but an avalanche caused by the explosion throws him over the edge again, without a rope this time. Monique, who survives because she was still under the cliff’s edge, pulls herself up despite several broken fingers, and radios base camp that Cyril has been killed.
Back at the military station, the nitroglycerine canisters are exposed to sunlight and explode. Base camp tells the teams to get their cases of nitroglycerin into the shade. Kareem and Malcolm do so, but, while resting after covering the cases, the leaked nitroglycerin is eventually exposed to sunlight and explodes, killing the two.
Meanwhile underground, McLaren is severely injured, with a broken leg and ribs, and he has lost his dexamethasone. Annie shares her dex with him, but Vaughn refuses it, stating that every climber should take care of his/her own supply or risk death. Annie risks her life to reach Ali’s body and backpack, and manages to obtain additional dex for both McLaren and herself, but Vaughn tells her that McLaren is unlikely to survive, and therefore, they should keep all the dex for themselves.
The nitro explosions have shaken loose some ice, and Wick finally discovers his wife’s body in a glacier. The empty dex box near his wife’s suggests that Vaughn lied and stole her dex, thus ensuring his own survival while leaving her behind to die from pulmonary edema.
Monique joins up with Peter and Wick, and the three spend the night on the mountain. Peter is wary of Wick, fearing he might be more intent on taking revenge than in rescuing his sister.
Meanwhile in the crevasse, Annie falls asleep, and Vaughn kills McLaren with a dex syringe full of air to save the remaining dex for himself. Annie suspects Vaughn but decides not to confront him and instead to save her strength, as she is already suffering from pulmonary edema.
Wick awakens to find that Peter and Monique have gone already towards their destination, leaving him behind as they no longer trust him. Peter signals Annie their position, and Annie and Vaughn manage to mark the crevasse entrance by launching a homemade flare and using McLaren’s blood as paint. Peter and Monique use the nitroglycerin to blast a hole, enabling access to the survivors and are joined by Wick, who promises Peter that he will rescue Annie.
Wick descends into the cave and harnesses Annie, and although the weakened Vaughn thinks he is about to attack him, Wick attaches a harness to him as well. Wick and Peter attempt to pull Annie out of the crevasse, but an ice boulder falls, knocking Wick and Vaughn from the ledge in the crevice, and pulling Annie and Peter down.
Monique alone remains on the ledge holding the rope onto which the other four are hanging. To save Annie and Peter, and to fulfill his revenge on Vaughn, Wick pulls a knife from his pocket, says a Buddhist prayer, and cuts the rope holding himself and Vaughn dropping the two to their deaths.
Recovering at base camp, Annie reconciles with Peter, who finally pays his respects at a memorial for those killed on K2, including Kareem, his cousin Ali, Cyril, Malcolm, Tom McLaren, Wick, and his wife.