Pete Townshend was thinking beyond the confines of short pop songs even in the Who's earliest days. Released on their second album, A Quick One of 1966, "A Quick One While He's Away" is a nine-minute song in six separate parts. The story itself is rather simple: a woman has grown tired of waiting for her man to come home after he's been gone for over a year, so she has an affair with Ivor the Engine Driver. When her lover returns, she confesses the whole thing and is ultimately forgiven. The music is far from simple, and some claim it laid some of the groundwork for progressive rock. One section called for a cello, but when they couldn't afford one, they band simply chanted "cello" over and over again.
The song was a highlight of their concerts through 1970, and their version from The Rolling Stones Rock and Roll Circus in 1968 was so amazing that the Stones felt they had been upstaged and opted to shelf the whole film. The Who haven't performed the song since 1970, but Pete Townshend has played it at some of his solo shows.