Was it a staged song cycle? A solo cantata? A monodrama? As mounted by Sydney Chamber Opera, Pascal Dusapin's O Mensch was utterly compelling, but never ceased to be enigmatic. The text began with the famous “O Mensch, gib acht” (O man, pay heed) speech from Nietzsche’s Also sprach Zarathustra, followed by selections of the philosopher’s much less-well known poetry, including “Ein Spiegel ist das Leben”, written when he was in his early teens, and “Der Wanderer”. It is to be regretted that the list of poems was not provided, and indeed one could have wished for some more pointers to help with this unfamiliar musical fare than the single page provided of personal reflections from director Sarah Giles.

With only an on-screen translation as guide to the elusive verse, the audience relied heavily on the performers to induct us into Dusapin’s world. A column of light suddenly illuminated singer Mitch Reilly positioned on a landing between two narrow staircases. He exploited to the full his tiny space over the hour-long duration of the performance: starting in a conventional standing position, he took up a variety of postures, now curled silently sobbing in the foetal position, now lying stretched out on the steps, now sitting in the posture of Rodin’s Thinker.

While the assemblage of texts did not suggest a narrative in the manner of, say, Schubert’s song cycle Die schöne Müllerin, one could easily trace an emotional progression, as Reilly’s initially composed demeanour fractured and was re-formed. Disrobing himself of both jacket and eventually shirt, the singer conveyed moments of existential anguish and manic agitation, but also oases of serenity. At times, the whole felt akin to the descent into a troubled psyche in Schoenberg’s Erwartung. The lighting design by Katie Sfetkidis modulated colour and brightness with great subtlety to accentuate Reilly’s journey. In one sequence, quick colour changes were coordinated with a series of cartoonish static poses from the singer.

Much of Dusapin’s music involved the exploration of different sonorities, from still, elegiac passages to more abrasive or nervously nimble moments. One had little feel of regular pulse or specific tonal centre early on, but more rhythmic sections proliferated later. One section sounded something like a distorted tango, both in the recurring rhythmic groove, and the similarly repetitive pitch contour of the bass.

Just prior to this, one might have detected a shadowy allusion to the music of Wagner, the composer with whom Nietzsche was most intimately associated. The first few notes of the opening three phrases from the Tristan Prelude were sounded, shorn of the famous identifying chord, and dovetailing into new material. A line in the text at this point, “drink the poison from every balm”, suggests both a complex metaphoric reference to the fatal drink in Tristan which turns out to be a love potion, and of Nietzsche’s own complicated love-hate relationship with Wagner. The later arrival of the Tristan chord (again at the same pitch level as it is first heard in the opera) turned the covert reference into open homage.

Aside from such subtle references, Dusapin clearly does not despise old-school ‘word painting’, where the music offers a direct correlate to the meaning of the language. Reilly’s voice plunged to a low F at the words “Look down”, while towards the end a high falsetto tone was needed for the line “up there I see rolling seas of light”. In general, neither vocalist nor pianist was asked for much in the way of extended techniques, aside from the half damping of a low F in the piano to give it a hollow sepulchral tone in the last quarter of the work. The multiple repetitions of this note suggested a reference to Zarathustra’s midnight bell.

The cynosure of all eyes throughout, Mitch Reilly delivered the absorbing, committed performance that has become a hallmark of his many involvements with the company. His emotional range was extraordinary, and his voice answered the demands put on it. Jack Symonds was impressive as ever at the piano, and created a vital palette of carefully gradated tone colours. There seemed to be an almost flawless level of coordination between the performers, who have been working together since the very first days of Sydney Chamber Opera. The cumulative effect, as so often in SCO productions, was absorbing, making a mockery of those who would claim modernist music cannot speak to audiences. The sole break in the silent intensity of the listeners came when the singer declaimed “Onions, farewell”. Nietzsche and his prophet Zarathustra would surely have approved of thus momentarily killing the spirit of gravity.