This was one of Plant's first songs recorded by the band, and also marks the first appearance of drummer John Bonham's Chinese gong, which he set up as part of his drum kit in concerts. The gong appears in the middle part among Jimmy Page's guitar riffs. According to the book Hammer of the Gods: The Led Zeppelin Saga, Plant wrote this song reflecting on his affair with his wife's younger sister. In Billy Joel's 1997 appearance in VH1's Storytellers, Joel plunks this out as part of his medley-intro to "We Didn't Start The Fire." Read more on Last.fm.