Euryanthe is a beautiful maiden who is betrothed to Adolar, Count of Nevers, but is also loved by another young nobleman, Lysiart, Count of Forest. At a royal festival arranged to welcome the knight from the battle-field, Adolar celebrates her beauty, purity and faithfulness in rapturous song. Lysiart mocks his panegyrics, declaring that "faith can ne'er in woman's heart abide" and wagers all "the fairest of his father's land in France" that he can win Euryanthe's love. Adolar gladly accepts the challenge, risking all his wealth upon the maiden's fidelity. Lysiart departs, boasting that he will return with a love-token.

In the second scene, Eglantine, a befriended outcast, coaxes a secret from Euryanthe, promising with extravagant expression of affection never to reveal it. It is that she communes with the spirit of Emma, Adolar's sister, who when her lover Udo fell in strife, pressed a poisoned ring to her lips. She has told how the gates of heaven are closed against her for this deed and how they never will be opened until the ring from which she tasted death is bathed in tears of injured innocence. Eglantine, who is in love with Adolar, plans to use Euryanthe's secret for her own evil purposes. Meantime Lysiart comes with many fair words to invite Euryanthe to grace the festival of King Louis.

In Act II, we find Lysiart bewailing the fact that he has had no success in winning the favor of Euryanthe. He is inspired with fresh hope by the appearance of Eglantine, who has visited the tomb to steal the ring from the dead hand of Emma and proposes that it shall be used as a proof, not only of Euryanthe's unfaithfulness in love but also of that of which she is really guilty the revelation of the secret known only to her and Adolar. For thus assisting him in his designs, Lysiart promises to marry Eglantine. Euryanthe arrives at the feast and is warmly greeted by King Louis and his knights, who have small doubt of her trustworthiness. Great is the consternation when Lysiart announces that he has his proof and produces the ring. Adolar can see in it only an evidence of her utter perfidy and, relinquishing all his possessions, declares his intention of being henceforth a wanderer.

In the next act, Adolar leads Euryanthe into the forest to slay her. A huge serpent confronts them and Euryanthe tries to save her lover by throwing herself in front of it. He destroys the frightful creature and, remembering that Euryanthe would have died for him, refuses now to kill her but leaves her alone in its depths. Here the huge slain serpent and the distracted maiden are discovered by the king and his hunters. In answer to the king's questioning, she relates the story of Eglantine's perfidy. He is convinced of her innocence and promises that she shall yet be united to Adolar. Adolar returns to Nevers, where he meets the bridal procession of Lysiart and Eglantine and sees the ghost of Emma trying to indicate to him his mistake. Here also comes the king to inform them that Euryanthe has perished of a broken heart. In a transport of triumph, Eglantine confesses the incident of the ring as well as her love for Adolar, whereupon Lysiart stabs her. The hunters bring in Euryanthe restored to consciousness and the lovers are united, while justice is secured by the consignment of Lysiart to the hangman.

The music score of Euryanthe contains some of the most beautiful products of Weber's genius but the improbable and badly-constructed libretto prevented the opera from finding favor when it was first presented and has resulted in its complete disappearance from the operatic repertory. In the concert-room there is heard still frequently, however, the ever-charming overture and, occasionally, Adolar's romanza, "Unter blühenden Mandelbaümen" (" 'Neath the boughs of flow'ring Almond") and Lysiart's recitative and aria, "Wo berg ich mich" ("Where can I hide").