The extraordinary expedition of climbing doctors reaches a tense conclusion as Horizon follows Dr Mike Grocott and his team as they attempt to reach the summit of Everest and measure the amount of oxygen in their blood. The doctors findings could rewrite our understanding of the human body and help save the lives of critically ill patients in intensive care. Their greatest goal is to discover a genetic link that allows some to survive low oxygen when others die. But to do this they must go to the extreme. Standing 8850m in the sky, Everest is in the 'death zone' and by climbing into this hostile environment they will be putting their own lives on the line.