NOVA treks with a group of Himalayan climbers in their quest to reach the summit of Everest, along the way exploring in never-before-conducted tests how extremes of weather and altitude affect the human mind and body. Why do some people succumb so quickly to the ills caused by high altitude while others do not? Does exposure to extreme hypoxia—or lack of oxygen—take a lasting toll on the mind and body? Images of the brain scanned before and after the expedition may reveal truths about the physical traumas suffered in an oxygen-depleted environment, and give us new insight into why the tallest mountain in the world has claimed so many victims.