Every year, thousands compete in the world's greatest singing competition - that you've never heard of. At the International Championships of Barbershop Singing, passion is equaled only by raw talent, and the reward is not fame or fortune, but simply victory. American Harmony focuses on four quartets in the ultra-obsessive, zany, and heartfelt world of competitive barbershop singing. Each team is vying for top honors in what turns out to be the closest and most controversial victory in the competition's 70-year history. Max Q is the heavy favorite - a superstar quartet comprised of former champions. Looking to upset them is OC Times (The Heart-Throbs), Vocal Spectrum (The Rookies) and Reveille, an aging foursome that has been performing together for 30 years. This fascinating documentary captures all the behind-the-scenes drama of quartet life - from big egos to brain cancer - and all the glory that comes with competing simply out of love of the game.