Confusion has such lovely music! Sydney's pioneering Baroque and early classical opera specialists Pinchgut Opera offered Haydn's Armida as its 16th production and delivered the glorious sounds that lead the composer to believe that his last Esterházy opera was also his finest – it received an unusual 55 performances there between 1784 and 1788, as well as others around the Austro-Hungarian world at a time when novelty was the norm. But Pinchgut seriously failed to clarify character motivation and a plot that has the evil sorceress, Armida at its centre, based on Torquato Tasso's dramma eroico, Jerusalem Deliver’d, from which so many other composers chose to concentrate on her lover, the conflicted Frankish knight, Rinaldo.

And boy, is he conflicted! In Act II, he must make a dozen switches of allegiance as his heart is played by the Saracen Armida and his sense of duty is aroused by Ubaldo, his Frankish colleague-in-arms. But then we're never quite sure whether to sympathise with an Armida who is genuinely in love with Rinaldo or to boo an Armida who is just using him to defeat the invading Crusaders. At first, the prospect of his getting killed by his European confrères drives her to appeal to the gods to magically distract the Frankish army. By the end, she has revealed the inner demon and the source of her power in a magic myrtle tree, while her golden glitter has turned to black. Despite Rinaldo's toppling the tree, she still appears to have the power to strike down all and sundry, including her own uncle, the King of Damascus!

It's true that Armida's libretto doesn't help to clarify such confusions, encouraging imported American director, Crystal Manich to refer to it as “the director's tabula rasa”. But an audience for an opera rarity like this really needs a little more help to string the story together, and surely surtitles can be used creatively to fill the gaps. For instance, the word 'Crusader' was never used as far as I could see.

However, cast and orchestra – under Pinchgut co-Artistic Director Anthony Walker, now retiring to concentrate on his directorships at Pittsburgh Opera and Washington Concert Opera – carry on notwithstanding such uncertainties, delighting in the rarity of dramatically accompanied recitatives and the freedom that Haydn was able to obtain in the seclusion of Esterházy to experiment with a variety of structures in his mellifluous arias.

Heading a young cast is Rachelle Durkin, an Aussie coloratura specialist brought back from The Met, where she's already appeared in ten named roles. She gave Armida both steel and feminine passion. Even as she and the Swedish Rinaldo, Leif Arhun-Solén, are tearing each other apart emotionally, their music together is sweetly magic. One might have expected some tension between the traitorous Rinaldo and his fellow-Franks, Ubaldo (Jacob Laurence) and Clotarco (Brenton Spiteri). But they're clearly so blasted by mighty storm music and the spiritual force of a trio of veiled Wilis that they too are generous in their song-making. And Clotarco soon – quite justifiably – falls under the spell of the minor sorceress Zelmira (Janet Todd). For Todd's singing brought to mind the description, “a brilliant fresh voice, shot through with laughter, not large but admirably projected, with an enchanting high pianissimo”. And that was Walter Legge on first hearing Elisabeth Schwartzkopf!

Sadly Armida's uncle, the wicked Idreno (Christopher Richardson), rules Damascus and takes exception to this treasonable liaison, turning Zelmira (and the Wilis) into automata and confusing poor Clotarco who thought their instant love might last the opera out. I wonder whether Idreno could have had a little more of the Orient about him, rather than moustache-twirling panto baddie, to distinguish him from the 'Europeans'. For they, at one stage, argue that they've come a long way for a fair fight and don't think that all this magic is really very sportsmanlike. Perhaps a hint of Assad for Idreno? Though I wouldn't want the purist Pinchgut to follow in the wild footsteps of Peter Sellars who, in 1968, set his Armida in the Vietnam War.

Pinchgut – the name, by the way, derives from the tiny island in Sydney Harbour where the worst convicts were marooned to starve, and was chosen to reflect the opera company's tight budgets – performs in the city's brilliant Recital Hall. That was not intended for opera, so staging is always a matter of pinched guts. Designer Alicia Clements has done her best to create the two worlds of Eastern comfort and blasted battlefield, using two levels and a joining staircase. No more is needed, for the audience is there, devotedly, primarily for the music in a prime acoustic.