It was the British supermodel Twiggy who alerted Paul McCartney to the Welsh singer Mary Hopkin when Apple Records was looking for talent in 1968. The waifish soprano scored a huge worldwide smash with her first Apple single, the melancholy but rabble-rousing ballad "Those Were the Days," in late 1968; it actually knocked the Beatles' own "Hey Jude" out of the number one position in the U.K. Paul McCartney lent Hopkin a further hand by producing her first album and writing her second single, "Goodbye," which was also a hit. More comfortable with refined, precious ballads and f...