This was the first time Glyndebourne had staged Parsifal and they provided five hours of superb singing and awesome orchestral playing. Sadly, the potential impact was diminished by too many well-intentioned changes to the plot introduced by the Dutch director Jetske Mijnssen, which sometimes made what was already an elaborate plot occasionally unintelligible. I strongly suspect that Richard Wagner would not have approved.

The story, as Wagner wrote it, was based on a mixture of European myths concerning the Knights of the Holy Grail. Parsifal is the innocent hero who has the task of finding and returning to the knights the spear that pierced the body of Christ. Only a touch from that spear can cure the knights' leader Amfortas from the constantly bleeding wound he received from the sorcerer Klingsor. The wild and mysterious woman Kundry also clearly has a role to play in her role as a messenger of the Knights, but it is not yet clear what that role will be.

Like all good myths, this is mystical and complex, but Mijnssen's attempts to de-mystify and humanise it tend to confuse. First, Amfortas and Klingsor are portrayed as long-lost brothers, perhaps to help relate them to the story of Cain and Abel which is also added to this version of the tale. The mystical spear has, for some reason, been reduced to a small dagger, while still being called a spear, and the question of who will become King of the Grail Knights looks rather like a family squabble. Worst of all, the Knights of the Grail, dressed like priests, are seen incongruously descending on Parsifal and beating him up when he is expelled from their presence.

All this confusion made the first act rather unsatisfying, but the second act made up for it with some magnificent singing in a simpler scenario dominated by Kundry (beautifully sung by German mezzo-soprano Kristina Stanek), Klingsor (American bass-baritone Ryan Speedo Green) and Parsifal himself (Swedish tenor Daniel Johansson). All three demonstrated voices of immense power when needed, but also displaying subtle emotion when called for.

The second act also included the best touch from the director in displaying all the chorus of flower maidens as Kundry lookalikes, which gave a much needed injection of humour into the heavy drama. Though again I am not sure what this was intended to mean. More confusion returned in the final act, when reconciliation or redemption was achieved, though the simultaneous appearance of old and young versions of Klingsor and Kundry was also a little bemusing.

Apart from those mentioned above, two other exceptional performances deserve praise: 78-year-old English bass John Tomlinson was gloriously effective as the aged Grail King Titurel, while Canadian bass John Relyea sang the demanding role of senior Knight Gurnemanz in hugely impressive manner. This role is by far the longest in the opera, involving around 90 minutes of singing, but Relyea's powerful voice never flagged when narrating the story. The greatest praise of all, however, deserves to go to the London Philharmonic Orchestra providing five hours of Wagner's glorious music under their conductor Robin Ticciati. Sublime singing of magnificent music produced by an awesome orchestra. But as I said, the direction was dodgy.

Parsifal is playing at Glyndebourne on various dates until 24 June.

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