Sandy Irvine and George Mallory vanished during their attempt to summit Mount Everest in June 1924, and the mystery over whether or not they reached the peak endures to this day. On the snowy peaks of Mount Everest, the tallest mountain on Earth, the dark object in the snow stood out. It was not trash, a piece of equipment, or a protruding stone. It was a boot with a sock inside that clearly identified it as belonging to A.C. Irvine. In other words, it was the partial remains of Sandy Irvine, the 22-year-old climber who disappeared while attempting to summit...