If anyone ever wants to know how opera is different from spoken theatre, you could point them towards a few select pieces like Mozart’s Figaro, Britten’s Turn of the Screw and this crazy melodrama by Puccini, for lesson one. Figaro transfigures Pierre Beaumarchais’s French sex-comedy with trendy political seasoning into a manifesto for making the world perfect through love. Britten adds innumerable layers to Henry James’s labyrinth. Finally (no doubt on a less elevated level, but still) Puccini turns a lurid shocker, that could only possibly be redeemed by having Sarah Bernhardt playing its heroine, into a gut-punch of humanity crushed by malevolent political forces. It has gained immensely from the resonances that subsequent 20th century tyrannies have bequeathed us.

The purer-minded have always been a bit disturbed by how sheerly entertaining Puccini makes his dreadful tale, how hugely enjoyable the appalling Scarpia is with his vivid perversions. (Few can resist dressing him up accordingly, and indeed here he’s equipped with cute little leather fingerless bondage gloves.) There is a temptation to suggest some kind of psychology to chaps like Scarpia, because panto villains can seem a bit embarrassing in a show for grown-ups, but it never really works, and what’s the point anyway? He is (like Lavrentii Beria) a machine for destroying innocence who has wound up in the perfect job — he says everything he thinks, there is no mystery to explore. Quite rightly, Puccini gives in and hands the guy the most thrillingly horrid scene in opera, where he bellows out his cartoonishly carnal programme over the gigantic choir-and-organ Te Deum in the fabulously camp surroundings of a baroque Roman church. Brilliant! This is what we came for.

All directors long to put a bit of nuance into Tosca, in spite of Puccini’s micromanaging of everything through the exactitude of his musical drama and imagery. In the end, all that’s really left to tinker with is the body language (and stage design, of which more later). Tosca herself of course has to be massively hot, otherwise the simpering flakiness of her religious mania, plus her insane hair-trigger jealousy, would make her an immensely tiring girlfriend. Luckily boyf Cavaradossi is too sexually bewitched to care, to the extent that even when he’s about to get the chop, he still can’t think about anything except her tits. Again, not much room (or need) for manoeuvre.

It’s a long way round of saying that the secret of Tosca is to do the central things well, to admit you’ve got little choice and just hand yourself over to Puccini. At Northern Ireland Opera, starting with the Ulster orchestra conducted by the Brazilian Eduardo Strausser, things were very promising: a big, bright, forward string tone; plenty of Mantovani-style swoops and slurs; a real schwung to the first crashing chords and orchestral intro that raised the spirits.

Once you lose the love story, other weaknesses start nagging

Then Tosca arrived, a moment that Puccini gives the full build-up, with her excited offstage yelps of “Mario! Mario!” and a general sense of big things coming. The Russian soprano (actually Yazidi Kurdish) Svetlana Kasyan looks great and has a big dramatic voice, but she really needs to put in some work engaging with other persons who might also be on the stage. The singing itself was rather wild and wayward. From the first moment, this peculiar lack of connection had a serious impact on getting involved in the show. As mentioned, Tosca’s a handful, but you forgive a lot if she and the tenor at least pretend to be on the point of ripping each other’s clothes off. Alas, the dynamic between this Tosca and Peter Auty’s sturdy Cavarodossi was not exactly “love’s young dream”.

Once you lose that focus of the story — the harmless if full-octane love story that’s about to be buried under a ton of bricks — other weaknesses start nagging. An over-elaborate (but under-illuminative) set of a raised platform and large tunnel-like affair, differently adapted for the three acts, never really made its point, except maybe when Tosca mounted its scaffold-like steps in Act 2 to one of Puccini’s most freighted tunes. Auty, who never gives less than about 300 per cent, is nonetheless getting on a bit and sounded under strain at times — but he at least was trying to convey a nice mix of youthful frivolity and genuine ardour. Brendan Collins climbed right into Scarpia’s nastiest extremities, but missed out on his charm and black humour. Tosca, after eventually skewering him, dealt as coolly with that situation as with all others, as if her entire brain were Botoxed.

Not all was lost, by any means. Tosca belted out some really meaty top notes right at the audience in Frank Matcham’s newly restored, not-huge theatre, and the orchestra nailed all the soul-tearing emotions of Puccini’s score. There was Cavaradossi’s great prison aria “E lucevan le stelle” — containing opera’s motto-line “I die in despair!” — and Scarpia’s shattering Prince-of-Darkness entrance and nice Nazi-porn-décor dining room. In the amazing Roman dawn of Act 3, with its sounds and bells, the shepherd-boy song was delivered with nice assurance by Mollie Lucas. With all that and the smoke and torches and crushing foreboding of the finale, there was a lot of immediacy and serious punch here. You do really really need a Tosca who will grab the role and give it everything, though — musically, dramatically, emotionally. Anything less is frankly ungrateful.