An Italian city with a history stretching back to antiquity, soaring orchestral music, and a singer named Tosca: this is what awaited the audience in Florence’s Teatro Verdi on the evening of October 23, as the city’s largest opera house hosted the local premiere of an innovative new work. But the spectators had not gathered to hear yet another performance of Puccini. The year was 1913, not 1900, and it was the young mezzo-soprano Tosca Ferroni on stage that night—not the fabled (and fictional) Floria Tosca. Indeed, despite the venue, this was not to be an operatic performance at all. It was the first performance (if that is the right word) of...