Today's Vault request by Led Zeppelin marked the first and only time the band ever hired another singer to appear alongside Plant.  Robert's friend from English act Fairport Convention, Sandy Denny got the call to duet on The Battle of Evermore, found on their 4th album.  Still today, it remains a high point from the set, so "un-Zep" if you will, but after that album, anything worked!  Out of town?  Listen live on-line.

Plant performing The Battle of Evermore with Alison Krauss during their 2008 tour: