 Coldly implacable as Myrtha in "Giselle" and furiously malevolent as Carabosse in "The Sleeping Beauty".She displayed warmth, charm, and grace in such evocative works as "Liebeslieder Walzer" by George Balanchine, and "Dances at a Gathering" by Jerome Robbins.After many years on the stage of the Royal Opera House, Covent Garden, Mason began a new phase of her career as a ballet mistress and teacher.