Each year, thousands of people go missing in North America's forests, woods, and mountains. The Agenda explores the mysterious stories of those who disappear without a trace and the valiant, often eccentric individuals determined to find them, often to no avail. Steve Paikin speaks with Jon Billman, author of the new book, "The Cold Vanish: Seeking the Missing in North America's Wildlands." See omnystudio.com/listener for privacy information.