Twenty years ago, a young American hiker called Chris McCandless was discovered dead in an abandoned bus in the Alaskan tundra. His death became the subject of the best-selling book and film "Into the Wild." Now, PBS retraces Chris McCandless' actions to determine why he abandoned all links with his past, burned or gave away all his money, changed his name, and ventured into the Denali Wilderness. McCandless' own letters, newly available, as well as new and fascinating interviews, delve into the mystery that remains at the core of a story that has become part of the American literary canon and continues to captivate so many to this day.