 Adolar stakes his lands and fortune on the faithfulness of Euryanthe and demands that his friend shall show some proof of his victory should he win one.In her castle at Nevers, Euryanthe has given refuge to Eglantine de Puiset, the daughter of a mutineer.Eglantine is enamoured of Adolar, and under the pretence of friendship for her benefactor, she secretly determines to effect Euryanthe's downfall and rupture her attachment to Adolar.