Milan audiences were understandably sceptical when they heard in 1770 that a new opera by a certain 14-year-old Wolfgang Amadeus Mozart was to open on Boxing Day. It would surely be a disaster, they said. It's bound to close before the new year. They were wrong. What they perhaps didn’t know was that this young pup had already written three operas, several masses and 13 symphonies. Despite being six hours long (it included a ballet and probably incorporated music by other composers) Mitridate, re di Ponto ran for 21 performances, cementing young Mozart’s position as the next big thing.

Robert Murray (Mitridate)
© Craig Fuller

He was a genius in a hurry, of course, and as his star soared ever upwards his early opera sank into obscurity, re-emerging only in the late 20th century. Even now it's rarely performed, so it was a bold decision by Garsington Opera to present a new production by Tim Albery to a 21st-century audience (even if the piece is heavily cut to under two and half hours). But while this is not first-rate Mozart, it has tremendous value. It shows just how astonishingly advanced was the young composer, with so much of his scintillating score pointing the way towards the great riches that were to come in Lucio SillaIdomeneo and beyond.

The plot revolves entirely around the huge tensions within Mitridate's family. He is a combustible combination of weakness, vanity and cruelty, desperate to save his kingdom from Roman invasion, while suspicious of the motives of his two sons, Sifare and Farnace. Mitridate is betrothed to the widowed Aspasia, but she is in love with noble Sifare, simultaneously rejecting the amorous advances of the scheming, indolent Farnace, who is in league with the invaders. They all believe that Mitridate has died in battle, but he reappears, bent on vengeance for their duplicity. Much anguish ensues. This is not The Waltons.

Iestyn Davies (Farnace)
© Craig Fuller

Garsington has assembled a fine cast to fill these roles. Tenor Robert Murray excelled as the eponymous king, tackling with ease the audacious, unforgiving vocal leaps that the young Mozart assigns to him, indicating the ever-changing mood of this monstrous monarch who deludes himself that his small kingdom can overturn the might of Rome. Notable was his handling of the extended accompanied recitative, “Respira alfin, respira o cor” (Breathe at last, breathe, o heart), where he ruminates on his sons’ behaviour before launching impressively into a full-scale dramatic aria where he chillingly calls for Farnace’s death.

Elizabeth Watts (Aspasia) and Louise Kemény (Sifare)
© Craig Fuller

Soprano Elizabeth Watts gave a tender, sensitive reading of Aspasia, torn between her love for Sifare and her vow to marry the increasingly unhinged king. Her two big arias “Nel sen mi palpita” and “Pallid'ombre” were heart-breaking moments of pure despair, beautifully realised. Soprano Louise Kemény, in the trouser role of Sifare, was particularly impressive; impassioned yet dignified, the perfect foil to Iestyn Davies’ wonderfully louche, repellent Farnace, who brought a Handelian sense of line to his often furiously hectic vocal fireworks.

When Mitridate returns he is accompanied by Ismene, Princess of Parthia, who – heaven knows why – is in love with the ghastly Farnace. He cruelly rejects her, sending soprano Soraya Mafi into a carefully controlled downward spiral of grief, which quickly turns to exciting, flashing anger. Tenors John Graham-Hall and Joshua Owen Mills gave stalwart support in the smaller, yet vital roles of, respectively, Arbate, the nervous counsellor to the unpredictable Mitridate, and Marzio, the Roman tribune who thinks he has a pact with Farnace.

Soraya Mafi (Ismene)
© Julian Guidera

The English Concert sound impressively perky under the suave direction of Clemens Schuldt, with some fine individual solos, notably an extended obbligato from natural horn player Ursula Paludan Monberg.

If only the quality of Hannah Clark’s design would match the quality of the music. The stage is essentially bare, save for a sofa, a cabinet and some garden sheds on each side that bafflingly serve as entrances and exits. A stuffed zebra is present, for no apparent reason. Costumes are just odd: Aspasia is in Victorian widow’s weeds, Farnace sports a modern livid purple suit; Ismene wears a mad wig, an unflattering pink gown and a fur coat. Strange.

But where Clark scores is her inspired decision to make the huge back wall of the set advance imperceptibly towards us. As the tension grows the stage diminishes and claustrophobia increases. The walls close in on Mitridate and his warring family – and the Romans are at the gate.