The 21st-season opener profiles folksinger Peter Seeger, whom the Dixie Chicks' Natalie Maines calls a "living testament to the First Amendment." Spiced by archival photos and film, the bio features comments from Seeger, Maines, Bruce Springsteen and Bob Dylan, plus family members. Included: Seeger recalls Woody Guthrie; the Weavers and their blacklisting; Seeger's role in the 1960s folk-music revival, the civil-rights movement and anti-Vietnam War protests; and cleaning up the Hudson River.