contestants, and wins $100,000 prize at the intel international challenge fair invention. >> this could save lives. >> it is not every day you get an e-mail from a 15-year-old that comes with a detailed protocol with let's see what else, let's see where this goes. >> stahl: it is the story that has never been told. there were 105 in all, john riordon risking his own life, rescued in the last days of the vietnam war. even now, four decades later, when they see him, you know, they know he is the reason they are alive. >> thank you. >> stahl: and they call him "papa." how many grandchildren do you have? >> i keep using the number 105. but the grandchildren, don't ask me.