At this year’s Salzburg Festival, they staged The Magic Flute, which is normal—Salzburg is Mozart’s town, and the festival is rightly devoted to him. But they staged Das Labyrinth too, which is not normal. This opera, virtually lost to time, is a sequel to The Magic Flute—not by Mozart, I hasten to say, but by Peter Winter (whose name sometimes gets a “von”). More about all this in a moment.

The Magic Flute was given an unusual production. We were looking at some medical clinic, or asylum, or other institution. People stood around in white coats, making notes on clipboards. The Three Boys were little old men, looking like Montgomery Burns from The Simpsons. Had some experiment gone awry? At the end of the opera, Sarastro and the Queen of the Night wrestled on the floor, in a great struggle. No doubt the stage director, Jens-Daniel Herzog, was communicating important...