Knowledge proves empowering. Hannah begins to dress as a woman, is recognized as such and starts to take hormones. The emotional core comes later, unexpectedly. On her first Christmas away from home, Hannah flirts with her first male admirer in a coffee shop, while Ms. Kaminsky tenderly spins a viola-and-cello homage to the carol “O come, O come, Emmanuel.”

Yet violence is depicted unflinchingly, in a way that shows the importance of community. “Hannah after” is assaulted as “Hannah before” names those who did not survive similar attacks.

In an extended final scene, Hannah retreats to rural Norway, joking that personal transcendence surrounded by nature makes for a trite ending. She revisits her youthful traumas and writes postcards in a hand neither male nor female, just her own. She resolves to return home, her earlier male self now shadowed, carrying the bags.

The dual personality is clearly not ideal. Even so, “As One” forces you to think, simultaneously challenging preconceptions and inspiring empathy. Having Mr. Markgraf sing the first half, and Ms. Cooke the second, would be simplistic. Instead, both remain onstage, in a portrayal that recognizes the difference between “before” and “after.” The pair play with hopes and memories as Hannah negotiates the gender roles that society assigns. In Ken Cazan’s sparse staging, backed by scene-setting projections from Ms. Reed, the drama powerfully coheres, if only through the sheer force of Ms. Cooke’s charisma.

Ms. Kaminsky’s propulsive score for the Fry Street Quartet (led by Steven Osgood) has deliberately ugly moments of slips and slides, but generally pulsates in a light post-Minimalism. Notably, Ms. Cooke and Mr. Markgraf scarcely sing the same pitch. They coexist in intervals of varying awkwardness until the last line, when they sing strikingly in unison, “as one.” The text’s resolution depends on the notion that nature “just is.” A harmonic disturbance in the final chord suggests that Hannah’s fulfillment is not so complete.