The stage of the Agassiz Theatre is lined with cardboard columns. Strewn across the boards are big, half-painted set pieces--platforms akimbo, colliding, stairs aimed into nothing. I feel like I've walked into the closing scene of a tectonic morality play. Overhead, lights are just swinging into place over the balcony's edge. A crowd of performers is milling in the wings, brocaded and beribboned. In the pit a harpsichordist is bent over his instrument like a hermit at his orisons, wielding the tiny crucifix of a tuning key. A Cupid darts across the unclothed scene, her bow unstrung and one wing dangling. Someone jostles the stringed spear of a chitarrone, and two primped and padded militaries saunter on stage left. This is the dress rehearsal of Cavalli's Giasone, a baroque opera put on by the Harvard Early Music Society.

This is the dress rehearsal, but so far nothing seems ready. The scene is unclothed, the lights are out, the curtains malcoordinated. And yet as the tensed wrist of the harpsichordist travels across the tuning pegs, as the organ's pitch is finally affixed, as each musician is gathered into place, one senses that the real setting of this opera is here fully assembled.

The various architectural elements strewn about the dressing-room, the missing coats of paint--they're immaterial. Giasone already has a brilliant set: the violins, gut-strung and armed with baroque bows. The theorbos, or chitarrones, their halved-pear bodies flowering into tall, lyrical stalks. The melancholy viola da gamba and the haunting lirone shaped like early venuses. The blockflutes, the recorders with their warm and woody sound. The tiny baroque guitar, cradled like a courageous lap-dog, and the harpsichords, the harpsichords: banquet tables of the basso-continuo; two banks of oars pulling across the river of the ear.

This is the wealth and the worth of the opera--the strange and elegant improvisations of the continuo accompaniment, the endless intricacies and expression of the baroque orchestra.

Cavalli's Giasone, written in 1649, was sort of a blockbuster back in the Italian seventeenth-centry. The libretto is the usual pastiche of bickering deities and hobnobbing heroes, loosely based on the story of Jason and the golden fleece. Cupid and Fate are having a quarrel about which one most controls mens' lives, and they cause amorous chaos among the mortals. Giasone, Aegeus, Medea, Hypsipyle and their servants mill about in confusion and slapstick till at last, all sung out and snugly paired off they come to a happy closing.

But who cares about the story? What matters is the pure pageantry of it all--the piled wigs and gilded breeches; the lovestruck and the lunatic both mingling with gods. Fate is lowered from a trap door to walk with hunchbacks and adulterers. The fornicators wear brocaded robes and the chaste are no less adorned. What matters is the glittering recitative--the strange power of the counter-tenor and his haunting arias. The characters and their conflicts are secondary amusements; harmless distractions as each singer is guided or goaded into glory by the basso continuo. What matters is the music.

Edward Jones, the conductor, seems a little nervous. There's so much to be perfected before the opening this weekend. Armored Hercules is still wearing sneakers. The columns must be covered. The scene changes aren't quite together yet, and tonight a hasty Fate dangled down from the heavens in the middle of the sinfonia. It'll all be ready tomorrow, he assures me, but he's wrong entirely. Giasone is ready now, and it's beautiful.