Like many another piano student, she logged the requisite thousand hours before Carl Czerny's yellow-backed exercise books. But while Roberta Flack labored over knuckle-aching third and fourth finger trills, Rubina Flake—a daydream twin invented in early childhood—polished off Chopin concertos. At 13, Flack played the complete score of Handel's Messiah for her church choir. In her early 20s, she became a serious opera student. At that time Flake, presumably, was a diva at the Met. It came as no small blow then when Flack's vocal coach gently suggested a pop singing career.
Second-decade...