“How far back would you like to go?” Paul McCartney asks as we sit side by side on a small sofa in his office overlooking London’s Soho Square. The space carries a deep, resinous scent with something faintly churchlike in the air. A large green glass candle rests on the windowsill, and beyond it plane trees shimmer in the bright early afternoon light. McCartney purchased the building in 1974, and it has long housed his publishing company and various creative ventures. On another floor, members