Every decision Morris made here — keeping the instrumentalists onstage throughout, dressing the chorus and the main performers all in identical white shirts and trousers, using minimal sets, and having the “ghost child” who appears at the end not appear, but instead sing from offstage (in the voice of countertenor Daniel Moody)—worked to heighten the effect of this unusual Britten work. It was at once austere and moving, weird and familiar, and though its seventy minutes did not feel short, they all earned their keep.