The plot of Die heilige Linde defies summary, or even, it appears, synopsis. Though the leading Siegfried Wagner scholar Peter P Pachl contributes elaborate booklet essays on its ideas, the nomen-clature of its characters and its very equivocal position as a national opera, he gives no outline of the complicated plot before we plunge into the libretto. This is complete, with a translation that is rather insecure in tone. ‘The Nordics are downright nitwits,’ exclaims one of the characters: certainly the Germans act with remarkable obtuseness in the face of Italian cunning.

Set in the third century, the opera is a tale of many-layered conspiracy, intrigue, adultery, deception and impersonation involving the attempt of the German tribal chieftain Arbogast to forge an alliance with Rome, abetted by the devious Philo, acting as both political and sexual procurer. It culminates in the planting of a sapling to replace the sacred tree of the title that has been felled at the start, as symbol of the growth of the German nation, complete with invocations of Wotan and Thor.

Such allusions are risky, especially for a composer bearing the name Wagner. Excellently as he scores, and individual as his harmony can be, Siegfried fails to escape from the shadow of his father in much of the work, especially in the German scenes. Even the Italian Act 2, in which the intention is to suggest a lighter, sunnier manner, does not seem to have moved very far south from Nuremberg’s Festwiese and the benign eyes of the Mastersingers.

In Rome, as Philo works his conspiracy to link Autonoë to Arbogast, Volker Horn gets a sinister charm into his voice; Autonoë is charmingly sung by Katalin Halmai, wheedling her way into the arms of the hapless Teuton, bluffly sung by John Wegner. As Antenor, Roman Trekel makes the most of one of the longer and more distinctive arias as he persuades Autonoë to abandon her deceit and return to an honest life as a fisher girl with him in Miletus. Though Dagmar Schellenberger is a little light for the part, she does her best with Hildegard, the betrayed wife of Arbogast, and Thorsten Scharnke deals gracefully with another victim of deceit, the rather characterless Fritigern.

The score is continuous and largely unrhymed until end-rhyme comes into play so as to give the formal numbers the condition of aria; as well as handling the orchestra skilfully, Werner Andreas Albert paces the work so as to make structural sense of these. Die heilige Linde is not an easy work, but those who follow the increasing attention given to Siegfried Wagner will find plenty to interest them.