Humorist Roy Blount Jr. journeys down the Mississippi River to rediscover his southern roots, search for the spirit of Mark Twain,examine what's become of the nation's great river, and explore the literal and metaphorical "mainstream" of America. Along this great liquid divide, Blount discovers what holds this wildly diverse country together. Viewers meet such unforgettable characters as Leonard Kuhnert, a fisherman who catches giant catfish with his bare hands; Garrison Keillor, a renowned humorist who challenges Blount to a stone skipping contest; Winona LaDuke, an Ojibwe activist who ran twice for vice president of the United States; Kenny Salway, a reclusive environmentalist who spent 28 years living alone in the swamp; Leslie Eaton, a hippie nomad who makes a living reading palms; Bobby Wade, a colorful commercial fisherman trying to hold on to a business that's been in his family for three generations; and Wilbert Rideau, an award-winning newspaper editor serving a life sentence for murder.