A magic potion becomes both a blessing and a curse for two young people. Tristan is about to bring the Irish princess Iseult to Cornwall where she is to marry his uncle. A love potion has been prepared to get the arranged marriage off to a happy start. But when Iseult’s chambermaid pours it into the goblets of her mistress and the Cornish knight, they cannot hide their feelings, even if their love means treason to the crown. Sweet compassion instead of ecstatic love: Frank Martin’s Le vin herbé offers a new interpretation of the tale of Tristan and Iseult, which goes beyond Wagnerian pathos. Tom Randle and Caitlin Hulcup embody the fatal lovers in this production by Welsh National Opera.