Folk singer/weirdo Roy Harper was often seen with the group, and allegedly friends. He also sang lead vocals on a very popular (non-Zep) song - though few seem to know about it - which song?What year was 'Houses of the Holy' released?What song did Robert Plant refuse to sing after his car accident in Greece?Amaze your friends and family with all things related to the Led Zeppelin If you know your, there are 350+ questions sure to riddle even the most die hard fan Ready to take the challenge? Led Zeppelin Trivia Quiz Book today