Christmas carols sound like they have always been part of church tradition, but composer Howard Goodall sets out to show how often they were banned by church and state alike, and how far they drifted from their origins. He traces a single carol through as many as 400 regional variations, tracking how communities reshaped tunes and words to suit local taste. "While Shepherds Watched" turns out to have needed cleaning up by Victorian editors who found the original words too crude for polite congregations, and Goodall lays out the case that "O Come All Ye Faithful" may have started life as a coded Jacobite rallying song rather than a straightforward carol of praise. Performances break up the history throughout, with folk singer Bella Hardy and the choir of Truro Cathedral singing the songs under discussion so the argument and the music stay tied together. The film treats carols less as fixed relics than as songs constantly rewritten by politics, censorship, and local habit.