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. Now, as a new season dawns on the mountain, a team of doctors, rescuers, mountaineers, military special forces and an astronaut, return to save lives, and using themselves as subjects, decipher the deaths on Denali.