Caitlin Hulcup as Iseult and Tom Randle as Tristan in Le Vin herbé (WNO)
Caitlin Hulcup as Iseult and Tom Randle as Tristan in Le Vin herbé (WNO)
© Robert Workman

Three portraits of doomed love make up Welsh National Opera's spring season. Two, La bohème and Madama Butterfly, are the work of Puccini, a composer whose operas' naked passion has delighted audiences down the years. The third, Le Vin herbé, retells the ancient tale of Tristan and Iseult, and it couldn't be more different.

The music flows but never tingles, the sound gels with exquisite charm but rarely expresses character, yet the cumulative impact over 110 uninterrupted minutes is immense. In depicting extreme human emotions through cool music, Frank Martin's opera-oratorio has superficial mood parallels with Debussy's Pelléas et Mélisande. Really, however, the two works have little in common. For a start, the central narrative role for chorus (intended by the composer as an ensemble of 12 singers but here sung, briliantly, by the full WNO Chorus) lends a distancing effect and reminds us that in the 1940s, the decade of its composition, Bertolt Brecht was at peak influence.

Martin's octet of musicians (seven strings and a piano) occupy centre stage while the conductor, James Southall, stands downstage centre where a diva's prompt box might be. There are no divas in WNO's company though, only robustly capable singers who serve the work.

Tristan is Tom Randle, a fine spinto tenor who seems to have a clause in his contract that he must remove his shirt in every show. His beloved Iseult is sung, radiantly, by mezzo Caitlin Hulcup, and there are telling contributions from the likes of Rosie Hay as Iseult's culpable servant Brangien and Sian Meinir as the treacherous Iseult of the White Hands. (I know, two Iseults in one story. What are the odds?)

'A latent power to move the soul'

Martin quickly dispenses with the aspects that interested Wagner in Tristan und Isolde, namely the depiction of a love that transcends life's capacity, and instead focuses on the legend's intrigue of dilemmas and dichotomies. In Le Vin herbé (which roughly translates as 'Spiked wine', although 'Poisoned chalice' would be neater) love is both the harbinger and provider of pain. The bewitchment of Tristan and Iseult is an itch that no scratching can relieve; a living purgatory. "Being apart was neither life nor death" as the narrators say in Hilaire Belloc's standard singing translation. Their only hope of peace is to obliterate themselves.

When reviewing Hartmann's Simplicius Simplicissimus last year I was critical of Polly Walker's direction. Her work on that bore the hallmarks of a drama college project, and some of those characteristics are again present here. This time, however, they suit the material... mostly. Working on a bare stage with nothing but a modular gantry and Tim Mitchell's harsh, visible lighting sources to break the monotony, she creates satisfying character proxemics and paints some memorable stage pictures.

The aesthetic is overfamiliar, though, especially to regulars at theatre workshops. Everyone bar T and I is confined to wearing stage blacks, there's a houselights episode when the chorus spills out into the auditorium, and the only substantial props are church-hall chairs. These are carried on en masse by the choristers then removed single-handedly by Tristan in a gesture of agitation.

Southall and his players deliver a marvellously textured account of Martin's score with its dense but searching harmonies, persistently legato string writing and full-flavoured melodic lines. Yet for all its accessibility Le Vin herbé is a challenging score, even more so than, say, Berg's atonal operas, in that it's matter-of-fact with no apparent poetry. Stick with it, though, because the sense of absorption that grows across its duration has a slow-burn beauty and a latent power to move the soul. Martin is a wonderful, shamefully neglected composer whose version of The Tempest, Der Sturm, is a masterwork. And this one's not far behind.

Le Vin herbé tours to Bristol, Milton Keynes, Llandudno, Plymouth and Southampton until 25 April.