Marco Siffredi was the first person to snowboard Mount Everest in 2001, and was regarded by many as the world’s best snowboarder. Jeremy Evans explores the 23-year-old's mysterious disappearance as he descended Everest from the Hornbein Couloir, an unrelentingly steep, difficult to access route with a high failure rate. Using exclusive never-before-granted interviews with family and friends, Evans aims to solve Everest's last great mystery, exploring Marco's pursuit of a dream, his love of freedom and adventure, and how his French family was forever altered by his loss.