Violette Verdy, a French ballerina who performed for many years as a principal dancer of the New York City Ballet, coaches young dancers in a selection of roles created for her by the company's chief choreographers, George Balanchine (the "Mr. B." of the title) and Jerome Robbins. In the course of the coaching sessions, she reminisces about working with Balanchine and Robbins, recalling the points they emphasized and the images they used to elicit...