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Season 1 (Season 14) Episode 2 "The Devil's Chord"
(sh.itjust.works)
A good old fashioned Doctor Who Community
Alright, music nerds, help me out: what was the 'lost chord'? It wasn't the one Paul described in the canteen scene!
EDIT: It also wasn't the Hard Day's Night chord, or the A Day in the Life (which is just E Major, anyway) chord, which would be the obvious ones.
@frankPodmore @Trekman10
Well, I heard that there was a secret chord but Russell T. Davis couldn't clear it through Leonard Cohen's estate and it displeased the Lord.