Avid for steep slopes, Marco Siffredi (1979-2002) obeys only one rule: not to fall. This gifted kid with hair sometimes blond peroxidized, green or blue clashed in his valley: Chamonix, mecca of mountaineering. His thing was to go up and down on a snowboard. . 90 minutes September 8, 2002, altitude 8848 meters, rare oxygen, his head already brushing the sky and his snowboard running, Marco Siffredi, 23, rushes from the summit of Everest in the Horbein corridor and its slopes at 50 degrees . A year earlier, he had already made the first descent of the mountain on a snowboard. But there remains another corridor… more direct. It's not a challenge, just a reason to be... However, that day, at the top of the roof of the world, his trace is lost...