Gods and sea monsters; Lear-like storms; an Oriental princess. Tragédie lyrique-cum-opera seria: Handel and Gluck meet precocious genius. Idomeneo, composed when Mozart was a mere 25, was a groundbreaking score. This week, one of the most glorious casts ever assembled at Glyndebourne will be unveiled in a new Peter Sellars-Simon Rattle production that promises to sear the senses, crystallise character and give us more of this angst-ridden masterpiece than has been seen before.
Chasmic visions of a war-torn world (now there's a parallel), another grisly aftermath of the Trojan war, Idomeneo - first staged in 1781, when Europe's top-notch Mannheim orchestra moved to the Munich court - feels a million miles from the twee pifflings of much Neapolitan opera.
Philip Langridge sings the storm-battered hero who, like Agamemnon and Odysseus, struggles over the Aegean, from windy Ilium straight into a new disaster:
"En route home, Idomeneo makes a fatal promise to Neptune," Langridge explains, "Instead of sacrificing a couple of goats or a pig, he vows to kill the first thing he sees. Then he tries to wriggle out of it. But he's got it wrong: what he fails to see, and what Ilia finally points out to him, is that the gods are peaceable - they're on our side. That's why love wins through in the end: as with Abraham and Isaac, or even Jephtha, everything is finally forgiven.
"It's odd, isn't it - if we invoked the gods in a new opera nowadays, we'd laugh. Yet in a crisis, people still do it. When I first did the role (with Bernard Haitink and Trevor Nunn), I used to have to pretend, to act Idomeneo's emotional struggle.
"Now, in real life, I am a father: I mean, if you had to sacrifice your own kith and kin, you'd do anything to get out of it! Idomeneo refuses to tell his son the truth; he says, 'Neptune's made me be nasty to you. Each time I look at you, I'm filled with remorse,' and the boy thinks: 'Have I done something wrong?' Then he orders Idamante to clear off, with Elettra; and the silly lad goes off and kills the sea monster, which only makes things worse. If the monster had eaten him, problem solved! Idomeneo tries literally everything. But, finally, he has to go through with it.
"It's a brilliant story, so true to the way we live. It's Peter's idea, and certainly Simon has gone along with it, that everyone is suffering in some way, we're all going through trials in life. Idomeneo is sensitive and well-meaning, he's not a bastard, he's a simple bloke, a good person, a good king. We all make mistakes... but like politicians, if you tell even a very simple lie, it gathers speed, till you can't control it.
"We've all learnt from doing this opera. Peter is a director who, unlike some, really directs. He's brought all the arts together - the artist Anish Kapoor, Mark Morris as choreographer - mime, folk-dance. The lighting is incredible, and the storm, initially subliminal, is mind-blowing. Mozart's choral writing is phenomenal: you don't get choruses like that till Verdi! 'O voto tremendo' - it's extraordinary stuff. Or the 'shipwreck' chorus: where did he get those harmonies and progressions from?"
In his first aria, Langridge's Idomeneo agonises - like Vere in Billy Budd, or Titus over Sesto - over this unknown person who's going to be struck down. "You can hear it in the orchestra, the instrumentation, it's all there - terrible suffering. Seconds later, it turns out to be his own son. So that aria begins spiritually as low as you can possibly go, and then have to get lower still. It gets worse. By Act II, Idomeneo realises, 'Oh no, this lie has affected everyone: Idamante, Elettra and now Ilia, too'. He calls on Neptune, 'For heaven's sake, kill me!'. And it's catching: even his spin doctor (now there's a turn-up) offers himself in Idamante's place."
Langridge is leading a dream cast: the knockout Czech mezzo Magdalena Kozena as Idamante; the German soprano Christiane Oelze - Glyndebourne's former Susanna and Mélisande - as Ilia; and Anne Schwanewilms - last summer's gripping Euryanthe, and soon to sing her first Desdemona in Sweden - as the spurned, matricidal Elettra.
Is Elettra a victim, too? "She can't understand what she's doing on this island," says Schwanewilms. 'She came to Crete because she didn't know where to go after the killing of Aegisthus and Clytemnestra, and Idomeneo said, 'Come and stay with us'.
"In her first aria ('Tutto nel cor'), Elettra reacts quite passively and pathetically: she's suffering because of her feelings of guilt - she's not an actual murderess herself, but she's been the willing accomplice to Orestes killing them - and this guilt makes her crazy sometimes: she's in a kind of psychological crisis.
"She can be very extreme and aggressive; but she also has a lot of love to offer. She's expecting to marry Idamante, and was just becoming happy at the thought. Then Ilia, this Trojan princess, turns up. A rival. And that's when Elettra changes - her feelings explode, everything collapses. So her aria is about emotional collapse, I think."
Elettra's Act II aria ('Idol mio' - one of the loveliest pieces in all Mozart) is a different matter: "It's an outpouring of love," says Schwanewilms. "Everyone is searching for love in this opera, and they all handle it differently. But whereas in other arias there's scope for some great Spazierung - opening up - here, he just didn't want it. It's a simple song - in parts almost like a pop song! - like Euryanthe's 'Hier an die Quelle', but better observed.
"I just can't understand how a young man of 25 could write such brilliant music. Mozart singlehandedly created a revolution. It's untypical, mixed together - the structure, the music itself, the harmonies. After weeks of rehearsal, we're still discovering new things from this score. Unbelievable."
And performing with Rattle? "Simon is easy-mannered, accessible, you can talk to him; if an aria's too quick, he'll adjust to you. He wants the best possible result for everyone, he wants to help you to achieve your best. He really supports you."
"Even in the early days," adds Langridge, "during our first Idomeneo, Simon was enquiring, always searching for the truth. He has a wonderful way of judging a tempo: you'll think, 'That tempo is just a little bit too fast or slow', and he'll just ease it along for you, or pull it back if someone needs more time. He's interested in getting the very best from the singer.
"We've had the most gruelling few weeks. This opera takes everything you can throw at it, it really does. To my mind, Peter has come up with all the solutions. Take that line of Anne's, when Elettra sings, 'O qual contrasto'. I used to think that almost comic. Slighted lover, screaming on the periphery. But no, absolutely not. Her beloved is due to be killed: she can't bear that, even if he doesn't love her.
"Idomeneo finally forgives both himself and the gods. And it's interesting, because we're doing his last aria, which is nearly always cut, and Idamante's, and Elettra's, with her shivering recitative entire. It's some of the most stunning music in the whole opera. Every stick of this work is being done, and we believe that's a first."
'Idomeneo' opens at Glyndebourne (01273 813813) tomorrow at 4.30pm, and runs in repertory to 26 JulyReuse content