In one of opera's most powerful and haunted finales, 16 nuns are guillotined in Francis Poulenc's remarkable Dialogues of the Carmelites. This is no spoiler since after the stunning La Scala world premiere in 1957 no one talked of anything else. The opera is renowned for this ultra-dramatic final scene.

Aida has its tomb in which the lovers suffocate; Rheingold has its rainbow bridge with wailing mermaids; Boheme has its romantic death of Mimi; Tosca jumps off the parapets of Castel Sant'Angelo; Butterfly ends in hare-kiri; Salome, after kissing the dead lips of John the Baptist, is killed by the soldiers of Herod; Tsar Boris Godunov goes mad and topples down the palace staircase.

But nothing in all opera beats the nuns' procession up the steps to kiss Madame Guillotine. They sing a plaintive and heavenly “Salve Regina,” as each is killed – offstage – to the swish and thud of the blade's fall. Finally, only one singer is left, Sister Blanche, until she is cut off mid-syllable. There is a deafening silence until the orchestra takes up a gentle prayer as the curtain falls in benediction. As they say in opera, Gangbusters.

Director Francesca Zambello fumbles this iconic scene with a too quiet guillotine and cheesy set design. One of the mob opens a panel in the curved wall to reveal a gilded box at the top of the platform. When the nuns step in they are bathed in redemption's golden light, like contestants in some celestial game show. It's so literal, the scene's power is quashed in half. Thank God, we've got Poulenc's exquisite music and unfailing dramatic instinct to save the day.

Zambello does Dialogues no favors throughout. Hildegard Bechtler's rotating walls are minimalist and without atmosphere. The revolutionists run in with flags flying — just to do it; and the mob in Act III charges to the footlights to glare at us as if auditioning for Les Misérables. It's all without much imagination except the lighting design from Mark McCullough, which transforms the spaces within the non-stop walls with fiery red, warm ocher, or silvery white. He brings life and emotion to the dull set. Claudie Gastine's costumes are appropriately aristocratic for the Chevalier and his son, and appropriately nun-like for the convent. How can you ever make a whimple interesting? In an annoying piece of stage business, the nuns lug about a large cross in every scene, ungainly propping it against a wall or arranging themselves around it in decorative tableaux.

Disregarding all this, there remains Poulenc's distinctive masterpiece of a score and Houston Grand Opera's phenomenal cast. Both are wondrous.

No one sounds like Poulenc. When you hear him, he's instantly recognizable. His music sounds, dare I say, French. More so than Debussy or Ravel, which is diaphanous in texture like a watercolor, but Poulenc is earthy and grounded, incredibly melodious, with just enough tinge of modern harmonics to please the ear. His music can be grand, melancholic, jazzy, playful, or deeply sacred. It also fits speech; it's ripe for dialogue. And since this is a talky opera, weighty in themes of loyalty, faith, commitment, and community, it flows naturally. It sounds right for the words. It also sounds right just as music. He's a master at getting to the heart, whether it's an emotional outburst like the Old Prioress's death rattle, or the flighty little nothings of Sister Constance's chatter. But listen to the intermezzos between scenes. His tone paintings are vivid, pulsing with excitement, beautifully colored.

Natalya Romaniw, as fearful Blanche, who enters the convert for escape from the world, has an amber glow to her voice, rich and smooth.  Her brother, the Chevalier, the impassioned tenor Eric Taylor, describes her as a little rabbit. This she is not. She is solid and secure with a supple voice that carries through the Wortham with hurricane force. I would love to hear her Tosca. International star Christine Goerke, one the preeminent Brünnhildes of our day, imbues Madame Lidoine, the newly installed abbess, with an abiding tenderness toward her “daughters,” and steely strength when confronting the revolutionists. She tones down her natural force and allows the eternally patient abbess to shine forth. It's a heartfelt performance. Watch her hands as she comforts her charges before the execution. She really means it.

Now, for drama, there's no one better than soprano Patricia Racette, who always makes an indelible impression. Her Madame Croissy, the old prioress who's dying and is plagued with doubts about her failing faith at the end, is a masterclass in characterization. At her first entrance in an antique wheelchair she captures the gravity and desperation just by how she sits. She sings with emotion, too. What a pleasure to watch her. An added plus to her artistry is her impeccable diction. She might have had some rough vocal patches a few years ago, but those are over. She sounds magnificent. What an artist.

The other major roles are Mother Marie, a mother hen to Blanche, mezzo Jennifer Johnson Cano, and innocent Sister Constance, the young novice, soprano Lauren Shouffer. Cano has power to spare, a silky sheen to her resonant voice, and lively stage presence. She's one to watch. Shouffer we love to watch, too, ever since her student days in HGO's Studio Program. She bounces through Constance, giving her an aura of merriment and touch of the ethereal with her stratospheric coloratura paired with incredible technique. She's a joy to hear. As Shouffer plays her, Constance could be a dove with a halo.

Other notables in the cast include tenor Chad Shelton as the Chaplain; baritone Rod Gilfry as Blanche's father, the Marquis; mezzo Emily Treigle as Mother Jeanne; mezzo Sun-Ly Pierce as Sister Mathilde; and baritone Luke Sutliff as Dr. Javelinot.

Martyrdom is amply rewarded under maestro Patrick Summers who lovingly guides his forces into the lyric, radiant, and aching soul of Poulenc.

Dialogues of the Carmelites continues at 2 p.m. Sunday, January 16; 7:30 p.m. Wednesday, January 19, and Saturday, January 22. Houston Grand Opera, 501 Texas. Masks required. For more information, call 713-228-6737 or visit hgo.org. $20 - $210.