Turning a real-world friendship into a fictional rivalry, sopranos Sandrine Piau and Veronique Gens, who started their careers together under William Christie, have come full circle in this fascinating new project.

Two singers at their professional peak teaming up to bring to life two equally distinguished forebears? It’s a no-brainer. Add in colourful historical back-stories full of “libertinage and brief liaisons”, political scandal and bisexual exploration, and you have yourself a hit. Even if the music itself can’t quite match them for thrills.

Gens and Piau step into the silk shoes of Madame Saint-Huberty and Madame Dugazon respectively – the two era-defining divas of the 18th-century Parisian opera scene. Saint-Huberty was the queen of the Opéra, a singer whose “dramatic voice tending towards the mezzo-soprano register” and strong acting skills led her naturally to roles full of “grand and majestic passions”: queens, sorceresses and heroic Classical characters. The “light and slender-voiced” Dugazon, by contrast, ruled over the Opéra-Comique, making a speciality of “maidens, maidservants and shepherdesses” – roles in which the natural tenderness and delicacy of her delivery could shine.

While there’s...