More than mere accompanists, these players are participants in the drama, following the singer across the platforms with their instruments, and often whispering their own indistinct phrases. All of them on Wednesday, especially the flutist Claire Chase and the cellist Chris Gross, were compelling actors. (The soprano Alice Teyssier is alternating performances with the haunting Tony Arnold, whom I heard — and didn’t — and other members of the ensemble are also taking on instrumental “roles” through the run.)

Your attention is aroused all the more because you never quite hear what the performers are whispering. I kept picking up just parts of phrases: “I know I am,” “I wish I was somebody else,” “I said I’d give him access to the study room.” Mr. Lang’s piece invites you to savor the softness and bask in ambiguity. Several people in the audience shut their eyes and blissed out for whole stretches. Now and then I felt exasperated, especially when a performer would look right down at me and whisper something I couldn’t quite make out. But that may well have been Mr. Lang’s intention.

The piece builds to what could be called this unconventional opera’s climactic “Liebestod,” when the soprano seems to recollect, still whispering, “hot spirit kisses running up and down my spine,” “comfort and love.” At the end, after she leaves the stage, you hear her singing softly behind the curtain. The music suggests a wistful folk song, cushioned by plaintive harmonies and restless lines in the instruments.

But what was she saying?