The mission? To carry forward the musical legacy of a once-celebrated composer, as part of the duties of a musically ungifted oldest grandson. The stops along the way? The modernist frenzy of 1920s Vienna and Berlin and the artistic lassitude of 1940s and 1950s expatriate Hollywood. The culmination? The stage of an adventurous opera company in a little town in eastern Germany that was by turns an SS and a Stasi stronghold.