In the kingdom of Cornouaille on the Breton coast, the war between Prince Karnac and the inhabitants of the town of Ys is finally coming to an end. The condition of the peace treaty is that Karnac will marry Princess Margared. But her love for Mylio, who is betrothed to her sister Rozenn, will provoke a terrible tidal wave fomented by her thirst for revenge. Edouard Lalo found an inspiring libretto here, which he handled with a sense of theatrical urgency rarely achieved. The characters live out their passions, supported by vehement, colourful orchestration. The role of Margared, in particular, deserves to be numbered among the most successful in French Romantic opera. First performed in Paris in 1888, the work scored a triumph that was repeated at every revival in the provinces and abroad. Though barely two hours long, it teems with dramatic situations: Breton festivals, the supernatural appearance of Saint Corentin, a wedding accompanied by the organ, a tidal wave whose tumultuous billows are rendered to great effect. Le Roi d'Ys amply merited an ambitious staging at the Paris Opera, which it was unfortunately denied in Lalo's lifetime.