Alaska’s Mount McKinley, commonly referred to as Denali, is the highest and coldest peak in North America, and one of the deadliest mountains on earth. Each year more than 1,000 people attempt to summit it; many never to return alive. While some climbers die in accidents -- sliding off of icy cliffs, crushing bones against rocks, falling into hidden crevices, or losing their way and succumbing to the cold -- others, often in top physical condition, die from a strange disease that strikes at extreme altitudes. Now, as a new season dawns on the mountain, a team of doctors, rescuers, world-class mountaineers, military special forces and an astronaut, return to save lives, and using themselves as subjects, decipher the deaths on Denali.