In 2008, conductor Thomas Hengelbrock rediscovered Niobe, Regina di Tebe, written in 1687 by the Venetian-born, German-based composer Agostino Steffani. Although now little remembered, Steffani was a world-famous composer in his day and a man of many talents who became a diplomat and bishop as well as being a musician. Hengelbrock and director Lukas Hemleb staged Niobe at the Schwetzingen Festival, and they have adapted this production for the Royal Opera House and the Grand Théâtre du Luxembourg.

Niobe is the archetypal figure of human grief, and her story is a classic Greek tragedy of hubris and nemesis: she boasts that her fourteen children make her superior to the goddess Leto, whereupon Leto's two children Apollo and Artemis duly murder all fourteen. Niobe is turned into stone, but even the stone statue weeps tears forever. The story is an ancient one: in the Iliad, it's retold by Achilles in the poignant scene in which Priam begs him for the release of Hector's body. Luigi Orlandi based the opera's libretto on a longer version in Ovid's Metamorphoses.

I must confess to having approached the evening with mild trepidation: three and a half hours of an unknown early baroque composer on this bleakest of themes didn't necessarily sound like a fun evening. But I could not have been more wrong.

Steffani was a court musician, and this version of the Niobe story is about entertainment, not about tragedy and catharsis. Several romantic subplots are added as well as various comic asides, and where most of the Ovid poem dwells with some goriness on the individual murder of each child, in the Steffani opera, this is all over in a single flash of thunder. Niobe's transformation into stone and the suicide of her husband Anfione are beautiful and poignant, but mercifully quick: we move swiftly on to the wedding celebrations of the priestess Manto and the victorious Creonte's triumphal march. Steffani's music is a delight: full of life, constantly in motion and thoroughly infused with renaissance dance music. Where each number in a Handel opera might have many repeats and elaboration, Steffani has a greater number of shorter "ariettas" - the proramme notes tell of Niobe as being an unusual example of his operas in having fewer than 60 arias! This is very much opera in the style of a French court spectacular (Steffani spent significant time in Paris).

The musicianship in this performance was outstanding. Each of the nine roles has significant arias, and the Royal Opera assembled an all-star cast: not a single voice failed to enthrall. Véronique Gens was sensational as Niobe, producing clarity, warmth and lovely following of line. Jacek Laszczkowski, who sung Anfione, has a unique voice that ranges smoothly from tenor up to high soprano, sounding quite different from a conventional counter-tenor. It took me a while to get used to the voice, but his invocation of the music of the spheres (Sfere amiche) was spellbinding and I was rapt from then on. Hengelbrock's Balthasar Neumann Ensemble were lively and exciting throughout.

Steffani's original productions were thoroughly over the top affairs with vast numbers of special effects and giant stage engines that would overstretch the budget even of a high-spending house like Covent Garden. This production is a combination of opulence and minimalism which is improbable but highly effective. The sets are simple and mainly black, and the money is in the costumes, with acres of satin in black, gold and other colours. The stage effects are simple and brilliant - the production should win an award for the most creative use of helium balloons in opera.

Altogether, Niobe, Regina di Tebe was a huge treat and a most surprising evening. Here's one forgotten composer whose rediscovery is very welcome.